An MRI taken Saturday night revealed a torn meniscus, which will require surgery, manager A.J. Hinch said before Sunday's game against the Pittsburgh Pirates. Hinch said more tests will be performed Monday to check for further damage.
"That would be the best-case scenario for him, if it's just a torn meniscus," Hinch said. "Even though it's surgery, it's the least dramatic injury for a knee."
There is no timetable for Montero's return.
Montero suffered the injury while running out a grounder to the pitcher in the second inning of Saturday's loss to the Pirates. He was trying to avoid Zach Duke's tag when he landed awkwardly just before reaching the bag.
"I was running fine. I never slowed down," Montero said. "I was trying to kind of run him over. Then at that moment, I just felt something pop."
In four games this season, Montero was hitting .500 with three RBIs.
Hester is batting .333 with a home run and two RBIs in two games this season for Reno. He hit .250 with a home run and four RBIs in 15 games with Arizona last season.