CHARLOTTE, N.C. — Panthers coach Ron Rivera hasn't ruled out shutting down quarterback Cam Newton for the season because of a sore right throwing shoulder.

Rivera said Tuesday he plans to meet with Newton later in the week and figure out where he is "in terms of his physical state and mental state" before deciding if he will start Sunday against Atlanta.

"It's a tough situation right now," Rivera added. "Until I get a chance to visit with him I'm not going to speculate."

"I'm not looking forward to that conversation," Newton said after Carolina's 12-9 loss to the Saints on Monday night.

The eighth-year quarterback was noticeably frustrated talking about his lingering shoulder injury. The chiseled 6-foot-5, 245-pounder was a mere shell of his former self, struggling to throw the ball more than 10 yards down the field.

Newton's frustration stems from not knowing exactly what the issue is with his shoulder.

"I think the thing, when you talk to different people who can help you with it, is that there's not any magical surgery or whatever. It's just time," Newton said. "I've tried and done everything."

He's been taking anti-inflammatories, getting massages and trying acupuncture. He said there hasn't been a night that's gone by without having some type of work done on his shoulder.

Newton has been on a "pitch count" in practice for the better part of the season, often not throwing at all on Wednesdays and Thursdays during the week so he can rest.

Nothing seems to work.

He said the shoulder is not getting worse, but it's not getting better either.

However, the missed time in practice is affecting his timing with his receivers and he doesn't have the same zip on the ball as he did when he led the Panthers to the Super Bowl in the 2015 season, throwing for 35 touchdowns.

"I've been eager to go to (head trainer Ryan Vermillion's) office, weeks and weeks and weeks and kind of find out what it is. 'Did you find something? What am I supposed to do? What do we have to do?'" Newton said. "... It is what it was, just a lot of soreness and tension in the joints."

Without a diagnosis that demands he sits out, Newton has continued to play through the pain — and the frustration.

He doesn't even know if he will need another surgery after the season.

Rivera doesn't seem to know exactly what's wrong with Newton either, referring all injury-related questions to the team's medical staff. The Associated Press requested to talk to Vermillion through the team's PR department, but he was not made available for comment.

The Panthers (6-8) still have a very slim chance of making the playoffs — less than one per cent, according to the website fivethirtyeight.com —but have lost six straight and morale is low.

But that still could be enough to convince Rivera to stick with Newton another week.

"Believe it or not, there's a slim glimmer, so we'll see," Rivera said of the decision to start Newton on Sunday.

Center Ryan Kalil said "nobody is more frustrated than Cam."

"I've played a long time with the guy and he takes it personal. It's been a frustrating season, needless to say," Kalil said.

He called Newton one of the toughest players he's ever played with.

"I've seen the guy take hits and get his body up, game after game, season after season," Kalil said. "Hits that I have seen him take other guys wouldn't get up from. He fights through a lot of stuff."

Newton's stats were miserable against the Saints — 16 of 29 for 131 yards for a season-low 52.5 passer rating, by far the worst of the season. He was sacked four times.

If Rivera decides to sit Newton, Taylor Heinicke would get his first start.

When asked what good it does to play an injured Newton with little to gain, Rivera said Tuesday, "in all intents and purposes, we play to win."

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