Hafner went 0-for-3 with a sacrifice fly for Columbus on Saturday.
"The rainout last night slowed down his rehab a little bit," Acta said Monday. "We're anticipating we're going to activate him on this homestand. I just can't sit here and tell you [it'll be] tomorrow, or the day after. He's got to go through today's game.
"It's a matter of how he feels. He knows his body very well. It's a good homestand with a bunch of right-handers that we're going to be facing, but it comes down to how he feels."
Hafner hasn't played since May 23, and he had arthroscopic knee surgery on May 31. He's hitting .242 with six home runs and 23 RBIs in 39 games this season.
The Indians have a couple of options if Hafner is ready to return this week. They could go the typical route and send a player down to the Minors, or they could place outfielder Shelley Duncan on the paternity list for a few days. Duncan's wife is in the hospital and is ready to go into labor any day now. The couple is expecting twin boys.