O'Sullivan is listed as the Red Sox's starter for Tuesday's game against Oakland in the official game notes, Brian MacPherson of the Providence Journal reports.
Eduardo Rodriguez is expected to come off the DL later this week, which figures to make O'Sullivan's stay with the big club a brief one. O'Sullivan has a 3.00 ERA and 0.88 WHIP backed by a 32:5 K:BB in five starts (33 innings) at Triple-A Pawtucket this season.