CHARLOTTE — The Panthers have several issues on offense at the moment.

But in the short term, the physical condition of quarterback Baker Mayfield is near the top of the list.

Mayfield walked into his postgame press conference after Sunday's 37-15 loss to the 49ers with a walking boot on his left foot and said he'd have an MRI on his left ankle Monday morning.

Mayfield was injured late in the first half and hobbled to the sideline but was able to continue the game. He admitted being in pain, but as the team stares into a 1-4 start to the season and his own bet-on-himself season has gotten off to a rocky start, the physical symptoms began to recede.

"Yeah, I've got a walking boot on. My leg's not cut off, so I'm all right," Mayfield said. "Would love to be in a better position, record-wise. But keep pushing forward. It's not the time to put your head down and give up."

Mayfield finished the game 20-of-36 for 215 yards with an interception. And while the night offered few bright spots, there were a few plays made downfield. But mostly, he looks at this season so far as a missed opportunity for himself and the team.

The former No. 1 overall pick of the Browns, in a contract year, had plenty of incentive to prove to the entire league that he's closer to the 2020 version of himself in Cleveland than the 2021 version. The current version leaves plenty to be desired as well, but he said seeing a few near-misses only added to the emotions he felt after this one.

"A lot of frustration," Mayfield replied when asked about his takeaway from the game. "The more you think about it, angry because we haven't played to our capability, to be honest with you. That's the frustrating part. Have to translate it to Sundays, and win on Sundays. We work all week to come out on Sundays, and we've got to make the plays that are there."

Backup PJ Walker finished the last few minutes of the game, which head coach Matt Rhule referred to as "mop-up duty," and said it wasn't indicative of a change in plans. Asked after the game if he deserved to start, Walker replied: "I'm not answering that question." He and Mayfield are the only two quarterbacks on the active roster, with Sam Darnold yet to start practicing after his preseason ankle injury. Rhule said last week that Darnold is "not close right now."

But questions about next week will likely be answered once tests are done.

For Christian McCaffrey, the fact Mayfield continued to play in the second half at all was worth a nod.

"Props to Baker, for jacking his ankle up and playing the entire second half," McCaffrey said. "He's a fighter. It's not shocking. He's always been a fighter. For us, we just need to fix it. We're trying. We'll fix it."

There were moments when Mayfield put a few plays together, including a touchdown drive to start the second half. He also showed a flash of his attitude when asked if he took a pain-killing shot at halftime so he could return.

"No shot," Mayfield said. "Just tell yourself you feel better than you do and go out there and play."

Just before the injury, however, Mayfield made a mistake that might have been decisive.

His pass intended for McCaffrey was intercepted by 49ers cornerback Emmanuel Moseley and returned 41 yards for a touchdown, sinking the Panthers into a 17-3 deficit just before halftime.

Rhule called the pick-six a "gut-punch," and the Panthers did not recover.

"Yeah, it is, no doubt about a gut-punch," Mayfield agreed. "We believe in our two-minute offense. I double-clutched the ball, and when I released it, I don't think my feet were underneath me; I think the ball sailed on me a little. Just a game of inches. Probably about six inches too high for him to touch it or deflect it. Obviously, we'd rather have the completion, because he's open right there. Just try to be more in tune."

McCaffrey said, "I've got to make the play," when asked about it. But it was one of a number of misfires on the part of an offense that hasn't been in sync all year.

The Panthers entered the game last in the league in third-down conversions and went 3-of-15 in that category Sunday, driving their season average down to 24.2 percent (15-of-62).

Coupled with the 1-4 record, which came on the back of a seven-game losing streak to end last season, fans in the stands were upset and players were frustrated as they quickly filed out of the locker room. But McCaffrey, as he has done consistently, said he supported Rhule as the criticism mounts.

"You can say what you want about him, but I've been around a lot of coaches, and he's somebody who has always had my back," the veteran running back and team captain said. "You work hard, you do the right thing, and he'll have your back. That means something, for what it's worth. I'm pissed that we can't get it done for him and for the rest of the staff. We need to play better as players."

That includes Mayfield, but at the moment, there's no way to know whether or when he'll be able to help.