Red Sox pitcher Justin Masterson threw a bullpen session on Sunday, which he said likely means that his rehab start, scheduled for Monday, is probably off, per the Boston Herald.
Masterson is on the DL with a shoulder injury. The team wasn't sure whether to leave him in the minors for another start or work toward bringing him back to the Red Sox bullpen.
Masterson will likely throw another bullpen on Tuesday as he nears a return to the Red Sox.