Ann Arbor — A medical issue has sidelined Michigan cornerback Ambry Thomas, who was expected to play a major role in the secondary this fall, and it is unclear when he might be able to return to football.

Thomas was diagnosed with colitis and lost a considerable amount of weight, Michigan coach Jim Harbaugh said Tuesday night while giving an update on preseason camp. Thomas is not practicing now and has a long recovery ahead, although he has gained back the weight.

“If there isn’t setbacks, then there will be milestones he will be able to achieve with no timeline on that,” Harbaugh said. “It’s right now where he can be here, he can come to meetings, he could do conditioning and get treatment and we’ll find out where he is from a conditioning standpoint and how much football he can do over the next week to 10 days. When it’s determined what he can do, then that’s what he’ll do, and we’ll monitor for setbacks.

“The next milestone after that, he’ll be able to run at full speed and have conditioning and strength. The next milestone will be to start playing football without contact, again, always monitoring to see if there’s setbacks. After that, then he will be cleared to participate in contact, so those are the milestones he has to achieve without a timetable.”

Vincent Gray, according to defensive coordinator Don Brown and Harbaugh, has been getting a lot of reps at cornerback during camp in Thomas’ absence. @chengelis