The concussion was diagnosed when Brantley had tests Tuesday at the Cleveland Clinic. He was injured trying to break up a double play sliding into second base in the third inning Monday.
Brantley was removed from the game and passed an initial concussion test, but was sent to the hospital after experiencing discomfort during his pregame routine Tuesday.
The Indians are hoping they won't have to put Brantley on the seven-day concussion list. Manager Terry Francona said Brantley participated in some activities Wednesday, and Saturday is a realistic day for the outfielder's return.
Brantley is batting .323 and leads the team with 11 home runs and 46 RBIs.