Posted by ESPN.com's Ted Miller
Gronkowski, the centerpiece of the Arizona offense, could be out a week or longer, coach Mike Stoops told reporters.
He has left the team, which is practicing at Fort Huachuca in southern Arizona, and returned to Tucson.
Gronkowski caught 47 passes for 672 yards with 10 touchdowns in 2008. Backup tight end A.J. Simmons, a junior, has caught just three passes for 14 yards and a touchdown in his career.