O'Sullivan (knee) will make a rehab start with Triple-A Pawtucket on Thursday, Ryan Hannable of WEEI reports.
While his rehab seems to be progressing well, with the trades the Red Sox have made at the deadline, it seems O'Sullivan likely won't figure into the big league rotation, and may not even get a place in the big league bullpen. He'll likely offer rotation depth at Triple-A once his rehab is complete.