Fitts is scheduled to start Tuesday's road game in Philadelphia, Christopher Smith of MassLive.com reports.
After Hunter Dobbins (knee) was ruled out for the season due to a torn ACL, Fitts was called up from Triple-A Worchester on July 12 to fill his spot on the active roster. Fitts went unused out of the bullpen in Boston's final two games before the All-Star break, but he'll assume Dobbins' spot in the rotation to begin the second half. The right-hander could end up being in line for an extended stay in the rotation, as Tanner Houck (elbow) suffered a setback during his rehab assignment and now seemingly isn't a candidate to return from the injured list anytime soon.