Guillen, on the 15-day disabled list for the past two months after lingering inflammation in his shoulder forced him out of action, has been taking batting practice with the team the past few days. Not only has he felt fine doing so, he has taken extra swings.
"He's felt very strong," manager Jim Leyland said. "He hit a lot."
The Tigers haven't specified yet where Guillen would rehab, mainly because they have to figure out how to manage his stint around the All-Star break in the various Minor Leagues next week.
Triple-A Toledo is at home through Sunday, including a Saturday doubleheader, but then doesn't play again until next Thursday. Double-A Erie, by contrast, returns home Friday and plays through Monday before taking a two-day break. Class A West Michigan doesn't have a break, but is on the road until next Wednesday.
Guillen could conceivably start out with the Mud Hens, then transfer to the SeaWolves for Monday.
Considering Guillen hasn't played at all in two months, it won't be a short stint, so the breaks probably won't have a big impact on when he rejoins the Tigers. Leyland said earlier this week that he wants Guillen to get a heavy dose of at-bats, comparing it to Spring Training.
Still, it's clear Leyland can envision Guillen's return around or before the end of the month, comparing it to a deadline trade.
"Guillen could be our trade," Leyland said. "Guillen, if he comes back, could be the bat we're looking for. If it's Carlos Guillen, to me, that's a nice bat to have."
Jason Beck is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.