BALTIMORE -- Baltimore Orioles infielder Jorge Mateo left Sunday's game against Tampa Bay and entered MLB's concussion protocol after he was hit by a bat as teammate Cedric Mullins loosened up.

Both players were in the area around the on-deck circle when Mullins, who was batting one spot ahead of Mateo, appeared to catch Mateo in the back of the helmet while lowering his bat behind him.

"I was getting loose looking at the pitcher, and I did kind of like a circle stretch, just pretty normal stuff," Mullins said. "He was right behind me -- didn't even see him."

Mullins said he saw Mateo in the clubhouse kitchen and he seemed OK.

Mateo singled in his only at-bat in Baltimore's 4-3 loss to Tampa Bay. The infielder was supposed to bat second in the bottom of the fourth, but Ramon Urias hit for him.

"We're just waiting to see," manager Brandon Hyde said. "Get some more tests and see how he feels tomorrow."

It was an eventful day for Mullins. He robbed Jonny DeLuca of at least extra bases with a leaping catch at the wall in center field, but his struggles at the plate continued. After striking out to end the seventh with men on second and third, Mullins slammed his bat down so hard it broke.