Oklahoma defensive back Tre Norwood suffered a knee injury in the No. 4 Sooners' practice on Monday and it's unclear whether he'll be able to return to the field this coming season, sources told ESPN.
SoonerScoop.com reported that Norwood didn't practice Tuesday night and left the team's facility on crutches with a compression wrap on his left knee.
Norwood, a junior from Fort Smith, Arkansas, is one of Oklahoma's most experienced defensive backs. He started all previous 19 games, including 17 at cornerback and the past two at safety. He was working at cornerback, safety and nickelback in spring practice.
Sooners coach Lincoln Riley hasn't yet commented on Norwood's injury. Riley is scheduled to meet with media on Friday.
Norwood started each of Oklahoma's 14 games in 2018 with 58 tackles, 2 tackles for loss, 1 interception and 5 pass breakups. His interception came at Oklahoma's 1-yard line in the final minute of its 39-27 victory over Texas in the Big 12 championship game.
The injury is a significant blow to Oklahoma's secondary, which was a trouble spot in each of the past two seasons. The Sooners allowed 294 passing yards per game in 2018, which ranked last among 129 FBS teams, and had only 11 turnovers gained, which were the fewest in the program's history.
Riley lured former Ohio State defensive coordinator Alex Grinch to Oklahoma to shore up his team's defense. Former coordinator Mike Stoops was fired after a 48-45 loss to Texas in the Red River Rivalry in the sixth game last season.
In April, Riley announced that star linebacker Caleb Kelly had suffered a knee injury that required surgery. Kelly, a senior who started 24 games the previous three seasons, isn't practicing and it's unclear when he'll return. He could redshirt and return for the Sooners' final four games, which would allow him to retain a year of eligibility under NCAA rules.
The Sooners open the regular season against Houston on Sept. 1 (7:30 p.m. ET, ABC).