Right tackle A.J. Greene's season is over after suffering a serious injury to his left ankle in the fourth quarter of the Clemson game.

"It doesn't look like he's going to be returning this year," said Auburn head coach Gene Chizik, who did not give any further details.

Greene, who separated himself for the starting job at the end of August, went down in a pile as quarterback Cam Newton was sacked on a third-down play early in the fourth quarter. He didn't get up.

Medical personnel tended to him on the field and put his left leg in a brace before carting him off the field. Both Chizik and Dr. James Andrews went out on the field to check on Greene's condition, usually an indication of a serious injury.

Sophomore John Sullen replaced Greene in the lineup and will do so in his long-term absence, although junior college transfer Brandon Mosley is also an option.

"We'll re-evaluate it all," Chizik said.

Sullen was the runner-up to Greene in August for the starting right tackle job, showing progress after losing 40 pounds from when he reported as a freshman.

"The way it unfolded, I think he played well," Chizik said. "John came in and helped us win a football game."