Working home plate, Hickox was struck in the middle of his helmet by a foul ball off Cleveland outfielder Ben Francisco's bat in the sixth inning of the Indians' 22-4 win. Catcher Jose Molina quickly reached out to help steady Hickox as he staggered backward.
Hickox left the field for a moment, but remained in the game until second base umpire Tom Hallion replaced him behind the plate in the eighth.
Crew Chief Jerry Crawford says he believes Hickox spent the night in the hospital.
Umpire Mike Estabrook was set to fill in for Hickox on Sunday.