Montero, who took a hard foul tip off his face mask and had to leave Wednesday's game against Boston in the fifth inning, was going to be a game-time decision as to whether he'd be available to pinch hit after seeing how he handled batting practice, according to manager Eric Wedge.
"He's still not ready to start, but after he takes BP we'll see if he recoups from that," said Wedge. "Yesterday he was fine during BP, then he got a little dizzy taking ground balls. So if anything like that comes up, he's not ready to play."
Wedge said Montero would be evaluated further during the upcoming four-day All-Star break.
The 22-year-old finished the first half of his first full Major League season hitting .245 with eight home runs and 28 RBIs in 73 games.