Damien Woody explains why he thinks Cam Newton is not fully healthy after the Panthers' loss to the Buccaneers on Thursday Night Football. (1:39)

CHARLOTTE, N.C. -- Carolina Panthers quarterback Cam Newton's status is uncertain for Sunday's game at Arizona after he aggravated the left foot sprain he suffered in the third preseason game.

Coach Ron Rivera seemed almost resigned that Kyle Allen would be the starter for at least a game or two to give the franchise quarterback time to heal.

"The short term, yes, if that's the direction we have to head," Rivera said Tuesday. " ... Kyle is more than ready. Kyle did some really good things last year, showed us what he's capable of. Had a good preseason. He knows the offense. He knows it very well. So we feel confident about him."

Newton informed team officials of the injury after Thursday's 20-14 loss to Tampa Bay that dropped Carolina to 0-2. He spent the weekend getting therapy on the foot and spent Tuesday's practice working inside with the trainer rehabbing the injury while Allen and third-round pick Will Grier took all the snaps.

General manager Marty Hurney was asked before practice about the level of concern for Newton being ready for the Cardinals. He said that the situation was day-to-day.

Rivera offered little encouragement that his franchise quarterback would be ready for Sunday.

"It is what it is," he said. "The truth of the matter is, guys, we make the best out of it."

Rivera insisted that he didn't know exactly when Newton reinjured the foot and that he wasn't aware of it until after the game. That Newton came to him with the news, knowing the quarterback's competitive nature and desire to be on the field all the time, spoke volumes.

"He was low about it," Rivera said. "You could tell."

Rivera said there are no plans to bring in a veteran. Safety Eric Reid would welcome former San Francisco 49ers teammate Colin Kaepernick, who has been out of the NFL since he began kneeling during the national anthem in 2016 to protest social injustice.

Reid said that the fact that no team has called Kaepernick, particularly after a weekend in which Pittsburgh's Ben Roethlisberger suffered a season-ending elbow injury and New Orleans' Drew Brees a thumb injury that will force him to miss extensive time, said everything.

"It's purely blackball," Reid said. "How can there be any misconception about his willingness and readiness to play the game? ... To me it's clear as day. He's blackballed. I don't know how you justify it any other way."

Newton didn't blame the Tampa Bay loss on being injured, saying, "No matter that physical condition I am in, no matter what, foot, shoulder ... I didn't get the job done tonight."

Newton was not listed on the injury report before the game, but it was clear early that something wasn't right.

The 2015 NFL MVP had 15 off-target throws (10 over, five under), the most since Chicago's Mitchell Trubisky in Week 7 last season and the second-highest number in a game for Newton, according to ESPN Stats & Information research.

In two games, Newton has completed only 61% of his passes to receivers with 3-plus yards of separation, the second-worst percentage in the NFL and down from his 86% last season.

Newton was bad under pressure against the Bucs. He was 0-for-10 when under duress, with three sacks. That was the most such passes he's had in his career without a completion.

Newton completed 25 of 51 pass attempts for 333 yards and no touchdowns against the Bucs after starting the game 7-for-8, perhaps an indication of when the injury occurred. In two games, he has completed 56.2 percent of his passes for 572 yards and no touchdowns with one interception.

His completion percentage comes after a 2018 season in which he completed a career-best 67.9% of his attempts in his first year under offensive coordinator Norv Turner.

Newton, whose 4,806 career rushing yards are the most by any quarterback since 2011, also has been a nonfactor in the running game. He had two carries for no yards against Tampa Bay after having three carries for a career-worst minus-2 yards in the opener.

Should Allen start, it would be the second of his career. He started last year's finale after Newton was shut down for the final two games to deal with a sore shoulder that ultimately needed arthroscopic surgery.

Allen, undrafted out of Houston in 2018, completed 20 of 31 passes for 266 yards and two touchdowns and no interceptions in a win at New Orleans.

"He's got a really good arm, makes good decisions," Rivera said. "He just needs to speed himself up a little bit. One thing he has to get used to is the speed of the game. It'll be fun to watch him."

It'll also be time, Rivera added, to find out what the team is made of.

"That's part of why you go to training camp, to find out what kind of team you are," he said. "Does [this] change things? Yes, it changes things dramatically. If we're going to end up going with Kyle for a while, yes. We have to find out who we are with him as the quarterback. Going on the road, it's going to be a little bit of a challenge."