Newton sustained a left mid-foot sprain in the Panthers' third preseason game against the New England Patriots. He had foot soreness after the Panthers' loss to the Buccaneers on Thursday Night Football. Newton underwent treatment on the foot over the weekend and met with the team Tuesday morning to reassess the injury.
"He was low about it, he really was. He wants to compete so badly," Rivera said.
"It's tough. He wants to be out there for his teammates. I appreciate our conversation. He was very honest and he was up-front about it. He said he's going to do everything he can. We'll see what happens."
Newton did not practice Tuesday. Rivera said he has "no idea" when Newton will return. If Newton can't play in Week 3, the Panthers will star Kyle Allen. The Panthers signed Allen as a rookie free agent after the 2018 NFL Draft. Carolina also selected Will Grier in the third round of the 2019 NFL Draft. Allen won the backup job in training camp.
"I think Kyle's more than ready," Rivera said. "Kyle did some really good things last year, showed us what he's capable of. He had a good preseason. Had a whole bunch of ups, had a few downs ... He knows the offense. He knows it very well, so we feel confident about him.
Newton struggled in the Panthers' Week 2 loss, completing just 49 percent of his throws for 333 yards. Rivera said Newton didn't inform him of the foot issue until after the game. Newton said he "didn't it done" against the Buccaneers.
Newton has completed 56.2 percent of his throws for 572 yards and an interception in two starts this season. He has also been sacked six times in 2019.
The Panthers face the Arizona Cardinals at 4:05 p.m. EDT Sunday at State Farm Stadium in Glendale, Ariz.