The news comes one day after the Red Sox announced that Beckett would miss his scheduled start Sunday night with shoulder inflammation -- which manager Bobby Valentine said was "nothing serious," at the time.
"He's got some inflammation that we're going to calm down and take the time, whatever time it takes to do it," Valentine said (via Associated Press). "We thought in-between starts was enough. He could have gotten an extra day or two, I guess."
Franklin Morales will make the start Sunday, with Clayton Mortensen getting recalled from the minors as a corresponding move to Beckett hitting the DL. Morales has been good out of the Boston bullpen this season, but he hasn't started a game since 2009.
Valentine's initial plan was to start Clay Buchholz on in Beckett's place Sunday, but Buchholz felt he needed the extra rest. He's slated to start Tuesday against the Marlins.
Beckett, 32, is 4-7 with a 4.14 ERA, 1.15 WHIP and 56 strikeouts in 78 1/3 innings this season. He declined comment to reporters Saturday.