"There is no timetable set forth at all," Mills said. "When he does finally come back, we want him to be 100 percent to where he's able to play and he's ready to play every day -- instead of maybe play for a week and then he's so sore he's got to sit out four or five days or another week, or go on the DL another 15. We don't want that to happen. When he comes back, we want him to be ready."
Berkman, who is not with the team on the six-game road trip to St. Louis and Chicago, told MLB.com on Sunday that he is hopeful he can return to action when the Astros return to Minute Maid Park on April 20.
Mills wants Berkman, who hit .274 with 25 home runs and 80 RBIs a year ago, to come back and stay in the lineup.
"The thing is, some days he comes in and he feels real good, and then they try to increase the activity -- and all of a sudden, it's not there," Mills said. "So I think what we're looking for is maybe to get a little stability in that process and in his program to where he feels a little bit more comfortable to get through it."