Masterson will likely be placed on the disabled list, Scott Lauber of the Boston Herald reports.

Masterson's arm is reportedly suffering from fatigue, though no there's no specific injury related to it. Steven Wright or Robbie Ross Jr., would be the likely candidates to take over his spot in the rotation.

Red Sox manager John Farrell would not commit to Masterson making his next start after the right-hander was shelled for six runs on six hits (two homers) and a walk in 2.1 innings in Tuesday night's loss to the Athletics, the Providence Journal reports. "Clearly, he's not right," Farrell said.

Masterson said he feels fine "other than not making good pitches," but Farrell intends to put the pitcher through some medical testing between now and his next scheduled start. Tuesday's shellacking comes six days after Masterson permitted six walks and seven hits in 4.1 innings against the Rays. Steven Wright came on in relief of Masterson, throwing 5.2 innings. He is a candidate to replace Masterson in the rotation.

Masterson (2-1) was awful Wednesday, putting 14 men on base -- seven hits, six walks and a hit batsman -- and allowing four runs over 4.1 innings. He struck out just one batter and threw a wild pitch.

With all those baserunners, Masterson was lucky to get away with only four runs on his record. He's been highly inconsistent in the early going, compiling a 23:18 K:BB and 5.18 ERA over 33 innings, leading to the unavoidable conclusion that Masterson simply isn't a very good pitcher anymore. His formerly mid-90s fastball has descended well into the 80s, and there are precious few (if any) optimistic peripherals to point at.

Masterson surrendered two earned runs on six hits, walking three and striking out two over six innings on Friday.

Masterson pitched well on Friday as his offense struggled to provide him run support. He earned the no decision and brought his ERA down to 4.71.

Masterson struck out six and walked three while holding the Orioles to one run on three hits over five innings en route to his second win of the season Monday.

Although he struggled to get ahead of hitters in Monday's start (eight first-pitch strikes to 21 batters faced), Masterson avoided damage getting outs on the ground and missing bats while working around the trio of walks. As part of a two-start week, Masterson will face the Orioles again Saturday at Camden Yards.

Masterson gave up seven earned runs on eight hits and three walks with four strikeouts in 4.2 innings Tuesday against the Nationals.

This was pretty disappointing following Masterson's strong first start of the season against the Phillies last week. Of course, that may be the problem. In his first outing he was facing one of the worst lineups in baseball and Tuesday he faced the team that was favored in the preseason to represent the National League in the World Series. Boston has too many young internal options to allow Masterson to languish in the rotation if Tuesday's outing becomes a trend. He will have a chance to bounce back Monday against the Orioles, but it might be best to take a wait-and-see approach in most formats.

Masterson allowed two runs on three hits and two walks while striking out seven in Thursday night's 6-2 win over Philadelphia. He threw 95 pitches, 64 for strikes.

Masterson was given a six-run lead in the third inning, which helped, but he was on point Thursday. In addition to the seven strikeouts, he induced seven ground ball outs and threw strikes with all of his pitches. Not every night will be this good, but Masterson's pitching for a team with a good offense and six runs will be good enough to get a win most nights.

Masterson will start the third game of the season against the Phillies.

Masterson slots in behind Clay Buchholz and Rick Porcello in Boston's rotation.

Masterson allowed one run on five hits and a walk while striking out four in 5.2 innings in Monday night's game against the Twins.

Masterson was able to extend himself a bit, getting up and down six times and throwing close to 100 pitches. He's made a case for himself to be the No. 3 starter behind Clay Buchholz and Rick Porcello.

Masterson threw 80 pitches over five innings against minor-league competition Wednesday, the Providence Journal reports.

Masterson had a rocky first inning, giving up four runs to the Single-A hitters, but settled in after that. He said he felt strong -- better than he did in his last outing. There's still an issue of reduced velocity this spring, but Masterson feels he's nearly ready for the regular season.

Masterson allowed one run on four hits and two walks while striking out one in four innings against Baltimore on Friday.

Masterson bounced back from an unsettling outing his last time out, inducing nine groundball outs, but his fastball velocity still isn't up to where it was in 2013. Various reports indicate different velocity figures, but he sat in the high-80s for most of the game and dialed up on pitch to 92 mph. He threw 76 pitches Friday and has two or three more starts. He felt he was better Friday but still needs the work to iron out the heater.

Masterson had trouble finding his arm slot Sunday and gave up six runs on seven hits and two walks in 3.1 innings in a game against the Phillies, WEEI.com reports.

With his arm slot off, Masterson couldn't establish normal velocity and was susceptible to left-handed hitters who hit two homers off him. But only in baseball can someone come out of a performance like that with optimism. Masterson said he feels much better this season than he did last year at this time.

Masterson logged three scoreless innings, striking out four while not surrendering a hit in Tuesday's game against the Rays.

The Rays had a split-squad day Tuesday and sent the B-teamers to Fort Myers, so Masterson's sterling effort needs to be viewed in that context. Still, the right-hander has tossed five scoreless innings to date. With some expected tweaks coming to the rotation, Masterson is line to pitch the third game of the season in Philadelphia.

Masterson made his spring training debut Friday night, giving up one unearned run on one hit and a walk in two innings against Miami, WEEI.com reports.

Masterson kept his sinker down for the most part and induces groundball outs. He's happy where he's at this spring, a marked difference from last season when he didn't feel right after suffering an oblique injury in 2013.

Masterson had a bullpen session at JetBlue Park in Fort Myers and reported "nothing hurts" afterwards, WEEI.com reports.

The significance of his "nothing hurts" comment is that Masterson didn't feel this way last February when he first threw bullpen sessions following a September 2013 oblique injury. He said he didn't prepare himself properly leading up to the 2014 season, a year in which Masterson finished with an ERA of 5.88 in 25 combined starts between Cleveland and St. Louis.

Masterson agreed to terms with the Red Sox on Thursday, ESPN reports.

After opening the season as the Indians' ace, Masterson experienced knee issues that landed him on the disabled list. After a deadline deal that sent him to St. Louis, the Cardinals made the call to move him to the bullpen, where he posted a disappointing 3-3 record and 7.04 ERA. It's unclear how the Sox intend to use Masterson, who began his major league career in Boston, but he'll likely be given an opportunity to prove he can return to a starting role.

Masterson has been moved to the bullpen, MLB.com reports.

Manager Mike Matheny has yet to name a starter for Thursday's opener against Milwaukee, but he has ruled Masterson out as an option, meaning it will be either Marco Gonzalez or Tyler Lyons. Masterson gave up five runs on six hits over 4.1 innings Saturday against the Cubs, marking the fourth time he's given up five runs in six turns with St. Louis.

Masterson was hit hard in the first game of a double-header with the Cubs Saturday, lasting just 4.1 innings and giving up five runs on six hits and a walk while striking out five.

Three of the six hits were home runs as Masterson's struggles continue since being acquired in late-July. His spot in the rotation is definitely in jeopardy at this point and with Marco Gonzales pitching well Saturday night, and Michael Wacha nearing a return, it's possible he may have made his last start of the season for the Cardinals.

Masterson will likely pitch only from the stretch in an effort to simplify his delivery, the St. Louis Post-Dispatch reports.

Masterson has a 7.43 ERA in five starts since the Cardinals acquired him in late August. He'll abandon the windup in the hopes of saving his spot in the rotation.

Masterson struggled through three innings Sunday against the Phillies, allowing five runs on six hits and two walks.

Masterson struck out three on the day, but had another bad outing for the Cardinals, and now sports a 7.43 ERA with his new club through five starts. His command was a problem again, only throwing eight of 17 first pitch strikes on the day. Masterson will look to turn things around when his next scheduled start comes Saturday against the Cubs.