Santana was removed from Thursday's Grapefruit League game against the Yankees due to left knee discomfort, Alex Stumpf of DKPittsburghSports.com reports.
Santana slipped on the infield grass while attempting to field a flyball and was removed from the game immediately. He's still undergoing testing on the injury, so it's unclear if he'll be forced to miss additional time. If Santana misses any regular-season contests, Connor Joe is a potential beneficiary.