Lamet will swap spots in the rotation with Luis Perdomo, pushing his next start back to Saturday against the Tigers, MLB.com's AJ Cassavell reports.
There is no official word on why the change was made, but Cassavell speculates that it was to align the rotation so that the rookie receives extra rest over the All-Star break. Lamet has struggled through five starts (7.50 ERA), but he has flashed upside with 37 punchouts over 24.0 innings.