According to whoever writes the team reports picked up by USA Today and Yahoo, it's a blood count issue:
"--QB/WR Phil Bates has not practiced in two weeks as Ohio's medical staff tries to get a handle on a blood count problem with the senior. When healthy, Bates will be a potent weapon as either a running option at quarterback or one of the Bobcats wideouts."
http://www.usatoday.com/sports/college/football/mac/ohio.htm