Cain will start Thursday's game against the Cardinals in place of Madison Bumgarner (illness), Alex Pavlovic of NBC Sports Bay Area reports.
Bumgarner was a late scratch due to flu-like symptoms, so Cain will step in to make a spot start in his place. The 32-year-old Cain owns an unsightly 5.35 ERA and 67:43 K:BB across 21 starts (109.1 innings) this season. He's expected to return to the bullpen following Thursday's outing.