Contreras was removed from Thursday's game against the Cubs after getting hit in the head by Ian Happ's backswing, Derrick Goold of the St. Louis Post-Dispatch reports.
Contreras was bleeding from the right side of his head and went through concussion protocols on the field before exiting with trainers. The Cardinals will take a closer look at Contreras and provide more information shortly, but it's possible the 31-year-old backstop misses a few games.