Sanchez has been limited since straining his upper back swinging the bat last week. He took ground balls Saturday and was hoping to be able to swing a bat Sunday, but Mills didn't expect him to play in a game until Wednesday.
"We want to make sure we can get his back straightened out and get going," Mills said. "Right now, I don't have him playing until Wednesday I know he'd like to play before that, but I want to make sure he's 100 percent so we don't have any regress with that.
"It might not be a concern to him right now, but it's a little bit of a concern to me because he had it when he started Spring Training, although it's starting to act up, although it is in a different spot and a different kind of soreness."
Sanchez got the lion's share of playing time at shortstop when Tommy Manzella got injured in the middle of last season. He responded by hitting .280 with 25 RBIs in 250 at-bats.
"He's done a real good job defensively for us," Mills said. "He was solid last year, so that's not a big surprise. He's able to give you a good at-bat all the time, which is really crucial."