Cain was actually working on a no-hitter at the time -- though it was far from serious to consider the injury having derailed a possible no-hit bid. He was through three innings of shutout ball with three strikeouts and no hits allowed.
The severity of Cain's injury is unclear at this point, but if he were to miss a chunk of time, Yusmeiro Petit is a natural replacement. Not only did he take over for Cain Wednesday, but he's already made three starts this season for San Francisco.
Cain, 29, is 1-3 with a 4.05 ERA in eight starts this season. He's struggled with consistency and has also previously had a short disabled list stint due to slicing open his hand with a knife.