Mauer, on the disabled list since April 14, has hit .235 in the first season of a $184 million, eight-year contract. He had arthroscopic surgery on his left knee in the offseason and only played sparingly in spring training.
Assistant trainer Dave Pruemer said Tuesday there is no timetable for Mauer's return but the catcher is over much of the soreness in his legs and feels stronger.
Minnesota was 9-18 and last place in the AL Central before Tuesday night's game against the Chicago White Sox.
"We've done it before but we always had the other pieces in place," manager Ron Gardenhire said. "It's always tough going without your catcher and your three-hole hitter and all those things. That's never been an easy thing to replace or fill that hole. But when you have all your other parts working around it, it makes it a little easier to try to get through things. This has been really tough."
Right-hander Kevin Slowey, on the disabled list since April 9 because of bursitis in his throwing shoulder, threw about 65 pitches in his last rehab outing and could join the team when it goes to Boston this weekend. He likely will be in the bullpen.
Delmon Young, on the DL with an oblique strain, also is progressing. And second baseman Tsuyoshi Nishioka, who broke his leg early in the season, has gone to Florida and begun on-field activities.
Minnesota scratched designated hitter Jim Thome from the starting lineup because of a sore oblique. Thome is nine homers shy of 600.