Mixon is under investigation for allegedly assaulting an Oklahoma female student at a restaurant near campus early Friday morning.
Oklahoma players reported for preseason camp on Wednesday. The team's first practice is scheduled for Thursday.
The recruiting website Rivals.com rated Mixon No. 1 among running backs in the class of 2014.
Mixon was expected to compete for playing time right away.
OU Athletics statement: "Joe Mixon is not reporting for team activities at this time. We will continue to monitor the situation." — Oklahoma Football (@OU_Football) July 30, 2014
- Chris Johnson