Willis was the 2003 NL Rookie of the Year and a 22-game winner in '05, but is 1-4 with a 7.49 ERA this season while struggling with control problems that have intensified in recent starts. He walked eight in 3 2/3 innings in a loss at Pittsburgh on Sunday and has walked 18 in 11 innings over his last three starts.
Willis believes the problems are mechanical, not mental.
"I've talked to everybody and I don't feel like I have any nervousness out there," Willis said. "I've got so many moving parts that if one's out of whack from time to time it happens.
"This is not the first time I've had control problems, but I've been able to overcome it, so I'm not worried about it."
Willis has been his usual gregarious self during a three-game interleague series against the Cardinals, constantly joking around with teammates. He even punctuated many of his comments about going on the DL with laughter.
The team believes the cause of Willis' repeated control problems is deeper than just mechanical issues. Trainer Kevin Rand said Willis has been dealing with anxiety issues since spring training.
"What we're trying to do is put Dontrelle back in a position where Dontrelle can perform," Rand said. "As it stands right now it's not the Dontrelle Willis you expect to be pitching, but we see it's in there.
"We've just got to get to it."
Right-hander Alfredo Figaro was recalled from Triple-A Toledo on Saturday to fill Willis' turn in the rotation against the Brewers.
The 24-year-old Figaro, who'll be making his major league debut, throws in the mid- to upper 90s. The Tigers also considered giving reliever Zach Miner the start.
The Tigers have been in contact with Major League Baseball for guidance, and Rand said medical staff will meet in Detroit to formulate a rehab plan. Willis will remain with the team, at least for now.
"It does me no good to not throw," Willis said. "I'm just looking forward to doing whatever they need me to do to get my mechanics right."
Leyland is rooting for the 27-year-old pitcher, who spent time at the Class A level last year ironing out his delivery in his first season with the Tigers.
"Dontrelle is a great team leader and my heart aches for him," Leyland said. "I think there's plenty left in his arm. He's a competing son of a gun."