David Ausberry timetable uncertain

NAPA, Calif. -- The Oakland Raiders' training camp has claimed its first casualty as tight end David Ausberry, listed at No. 1 on the depth chart, will undergo an unspecified procedure on an injured knee Wednesday and "may be out for a little while," according to coach Dennis Allen.

There is no timetable for Ausberry's return, which vaults Mychal Rivera into the starting role while giving opportunities to Brian Leonhardt and Nick Kasa. Rivera started three games last year as a rookie, though played in all 16, and had 38 catches for 407 yards and four touchdowns.

A seventh-round draft pick who was a wide receiver at USC, Ausberry finished practice Saturday and, with Sunday's off day, Monday was the first practice Ausberry missed in camp.

He spent last season on injured reserve after suffering a left shoulder injury in preseason.

Oakland plays its first preseason game against the Minnesota Vikings on Friday.

"The sky's the limit with this offense," said Rivera, who had three starts as a rookie. "Expectations are high for me, this offense, and I'm excited to see what we can do."

Allen was non-committal when asked if the fourth-year tight end is expected back before the end of the preseason.

"We should be able to get him back at some point and time," Allen said. "I don't know how long that is going to be. We'll have to evaluate that as we go along."

The Associated Press contributed to this report.