OAKLAND -- Boston Red Sox pitcher Justin Masterson will miss his next start and probably is headed to the 15-day disabled list, manager John Farrell said Thursday.
No determination has yet been made about who will start in Masterson's place Sunday in Seattle, Farrell said, though he identified knuckleballer Steven Wright as a "strong candidate." Wright replaced Masterson with one out in the third inning of Boston's 9-2 loss to Oakland on Wednesday night and finished the game, allowing three runs on six hits in 5 2/3 innings.
Masterson was examined by the team's medical staff Thursday morning.
"There's not one specific area to the arm or shoulder that's a cause or reason why we've seen him lose velocity or reduced action," Farrell said. "There's some fatigue involved. I think it's important we allow this to calm down. We're going to need to test it at full speed at some point in the near future, but Sunday is out as far as Masterson is concerned."
Farrell said he expects to have a starter in place for Sunday's game by the time the Red Sox begin a four-game series with the Mariners on Thursday night. One possible candidate in Pawtucket, left-hander Eduardo Rodriguez, started for Pawtucket on Wednesday and was ruled out by Farrell for that reason.
Masterson was an All-Star for the Cleveland Indians in 2013, when he posted a 14-10 record and 3.45 ERA in 193 innings. But on Sept. 2 of that season in Baltimore, he strained his left oblique muscle, and the following season he dealt with shoulder impingement, which may have been related to the oblique injury, and inflammation in his right knee.
Since that time, with significantly diminished velocity, he has made 38 appearances and allowed 109 earned runs in 167 2/3 innings, an ERA of 5.85. The Sox signed him to a one-year deal for $9.5 million last winter, believing he would return to health, but while he has not missed a turn this season, his last two outings raised red flags with the Sox. He allowed 13 hits, 7 walks and 10 earned runs in those starts combined, his ERA shooting up from 4.71 to its current 6.37.
"If this were one start, that would be a different story, but the fact that this has been two consecutive starts, we've got to address some things," Farrell said.
Masterson's 2 1/3 inning start on Tuesday night in Oakland was the fourth time this season that a Red Sox starter pitched fewer than 3 innings, most in the majors, according to ESPN Stats & Information.
Farrell said the Sox were not using Masterson's pre-injury status as a basis for comparison.
"We're not trying to go back to 2013 and the power he showed that year," Farrell said. "This is a matter of just seeing the last two starts as drastically different from the first five this year."
Masterson had hoped to avoid a DL stint, saying he believed working through his current issues was better than being shut down.
"He's disappointed," Farrell said. "They don't want to be moving in this direction with the potential of being taken away from the active list. He's a competitor. He wants to be on the mound, and we want him on the mound when he's right or when he's shown us, like the first five starts.
"He accepted it begrudgingly, but at the same time we have to be realistic. Like I said, when you see it two consecutive times, that's a little bit different than a mulligan."