CLEVELAND (AP) — Case Keenum didn’t doubt Baker Mayfield’s toughness for a single second. He may have underestimated his tenacity.

“There were some weeks just to get him to the field was a small miracle,” said Keenum, Cleveland’s backup quarterback who will start for Mayfield in the Browns’ season finale on Sunday.

With the hope of recovering more quickly to get ready for next season, Mayfield is skipping Cleveland’s game against the AFC North champion Cincinnati Bengals to have surgery on his left shoulder.

Mayfield’s injury was a major personal setback for the polarizing QB, and while the Browns (7-9) won’t use it as an excuse to explain their sideways season, it was undoubtedly a factor in the team falling way short of its goals.

Keenum, who started for Mayfield and won against Denver on Oct. 21, admired how his teammates refused to give in to an injury that may have sidelined others.

“I did have a front-row seat to one of the gutsiest, toughest performances of a quarterback playing in a season that I have ever seen,” Keenum said. “His entire season he was battling a lot of things. He’s one of the toughest guys I know, and he’s a fighter.”

Mayfield finally surrendered after being sacked nine times in Monday night’s 26-14 loss to Pittsburgh. Coach Kevin Stefanski said Wednesday that Mayfield, who was placed on injured reserve, did not sustain any new injuries while being pummeled by the Steelers.

Mayfield’s surgery has been scheduled for Jan. 19 in Los Angeles. The operation will be performed by Dr. Orr Limpisvasti, team physician for the Anaheim Duck and Los Angeles Angels who examined Mayfield’s injury during the season.

Mayfield’s uneven fourth season has clouded his future in Cleveland. The Browns picked up his fifth-year contract option for 2022 but has not discussed a long-term contract extension with his agent.

And while there are certainly flaws in Mayfield’s game, there’s no debating his grit.

Keenum was impressed by Mayfield’s durability along with a willingness to keep playing despite wearing a restrictive shoulder harness to protect his shoulder from popping from the socket.

There remain questions as to why the Browns would continue to play an encumbered Mayfield, but that’s not Keenum’s takeaway.

“He came to fight every single day and pushed through a lot of adversity just to get on the field on Sundays,” Keenum said. “I already had a lot of respect for him, and it grew as the season went on.

“Yeah, unfortunate the way the season ended. Nobody wanted this, the way this has gone, Baker for sure. Nobody really wanted this, but it’s tough. It’s a tough football league. That is kind of the way it is sometimes.”

Keenum would know.

The 33-year-old has bounced around as a starter and backup. He understands the fragility of the position, which is why he’s not taking his second start this season — in a game with nothing on the line — for granted.

“We’re all excited to get out there,” he said. “This is the NFL. Are you kidding me? We are playing football in January. We are playing a kid’s game that we have been doing our whole lives. We’re all very excited. Ready to get out there, ready to work and put this season to bed on a good note.”

Keenum has had his own challenges in this extraordinarily eventful season for the Browns.

He had been on track to start against Las Vegas when Mayfield tested positive for COVID-19, but then tested positive himself.

The next week, Keenum and Mayfield remained sidelined before clearing protocols on Christmas morning and flying together on a private plane to Green Bay, landing just hours before kickoff.

“That was nuts,” Keenum said. “That’s definitely something I’m going to remember forever — that whole week of Christmas.”

Because he couldn’t practice or be at the team’s facility, Keenum had to be inventive in doing workouts at home. He even took his kids to a local park.

“My kids were over there freezing on the swings, and I am trying to run and do a walkthrough and get some footwork on this frozen old soccer field,” he said.

Days later, the whirlwind ended with him being whisked to Wisconsin and inside Lambeau Field.

“It was unbelievable,” Keenum said. “It was definitely something I have never experienced before and hope to never do again.”

NOTES: Stefanski didn’t rule out any of Cleveland’s injured starters, including RB Nick Chubb (ribs) or TE David Njoku (shoulder) or CB Denzel Ward (groin), for Sunday. … LB Sione Takitaki (shoulder) was placed on IR. … With backup RB D’Ernest Johnson on the COVID-19 list, the Browns signed RB Dexter Williams off Miami’s practice squad.