OAKLAND, Calif. — Fullback Oren O'Neal and wide receiver Drew Carter sustained left knee injuries in the opening minutes of Saturday night's game against the Arizona Cardinals and likely are out for the season.

Both stayed down for a while before being helped from the field by two members of the training staff. Raiders coach Lane Kiffin said Carter sustained a torn anterior cruciate ligament. The extent of O'Neal's injury isn't as clear.

"Maybe it's just a sprain," O'Neal said afterward.

Kiffin didn't sound as optimistic, saying the expected loss of O'Neal is "a big deal."

O'Neal was hurt on the opening kickoff. Carter was hurt four plays later at the end of a 7-yard reception.

The Raiders can't afford to lose either player, Kiffin said. O'Neal is a primary blocker on certain run plays and a core special teams player. Carter was being considered, along with Ronald Curry, for a starting spot opposite Javon Walker.

"We lost two significant parts of what our offense hoped to be," Kiffin said.