Case Keenum doesn't feel as though he has to do anything more than he usually does to prepare for his first start as a Browns quarterback Thursday Night at FirstEnergy Stadium.

That's because Keenum, a nine-year veteran, has prepared to play in every game since he joined Cleveland in 2020. With 71 career games and 62 starts under him, Keenum knows what it takes to be ready for game day, but the Browns haven't needed to call on him yet to put his preparation to the test

That changes Thursday.

The Browns announced Wednesday that Keenum will start in place of Baker Mayfield against the Broncos for Week 7. Mayfield, who started 51 straight games since he became the Browns' starting quarterback in 2018, was ruled out for the game as he looks to rest a left shoulder injury he's played through since Week 2.

Cleveland will miss Mayfield, but it has plenty of reasons to be confident in Keenum.

"I feel very ready," Keenum said Wednesday. "I've been ready. You don't have to get ready if you stay ready, and I've been ready since I've got here. I'm excited."

The Browns have always viewed Keenum as an ideal backup for Mayfield — he was one of the first free agents they signed in the 2020 offseason after they hired head coach Kevin Stefanski, who worked with Keenum as a quarterbacks coach with the Vikings in 2017. Minnesota clinched a playoff spot that season, a year highlighted by Keenum's "Minneapolis Miracle" play in the NFC Divisional Playoff Game where he hit Stefon Diggs for a 61-yard, game-winning touchdown on the game's final play.

In Cleveland, Keenum had a head start on the schemes, play-calling and overall feel of the playbook Stefanski implemented to improve Mayfield, the Browns' 2018 first overall pick. Mayfield and Stefanski have given Keenum ample credit for his work behind the scenes for being a mentor for Mayfield.

Now, Keenum will have a chance to show how well he can play under the familiarity of Stefanski.

"I've been right in the middle of it the whole way," Keenum said. "I'm built for this. This is what I've done my whole career, from not knowing if I'm going to start up until game time to not knowing who's out there with me, to introducing myself to players while I'm calling a play."

"I know these opportunities don't come around very often to be a starting quarterback in this league. Only 32 per week, so I'm ready to take advantage of it."

Keenum's last start came during Week 16 as a member of the Washington Football Team in 2019. He has a 62.3 career completion percentage with 75 touchdowns, 47 interceptions and an 85.1 quarterback rating.

For Thursday, Keenum will be in charge of commanding an offense dealing with injuries at nearly every position. In addition to Mayfield's absence, the Browns will be without their two Pro Bowl running backs in Nick Chubb and Kareem Hunt, who both are nursing calf injuries. WR Odell Beckham Jr. (shoulder) hasn't practiced this week, and Jarvis Landry (knee) hasn't played since Week 2 and is not certain to return Thursday, either.

Starting left tackle Jedrick Wills Jr. (ankle) and starting right tackle Jack Conklin (knee) also didn't practice Tuesday and were limited participants Wednesday. Both players did not play last Sunday against Arizona.

That makes the challenge even harder for Keenum, but he's ready to play with everyone on the offense — no matter who's healthy.

"It's always a great challenge," he said. "That's what this league is about. No one is 100 percent. After Week 1, no one is playing 100 percent. That's the hard truth, and that's why it's a grown man's league. We have a tough team from top to bottom and a tough head coach. We're ready to go."

Keenum expressed remorse for Mayfield, who has spent the Browns' last four games playing through pain that's lingered ever since he dislocated his shoulder attempting to make a tackle following an interception against the Texans. 

He knows Mayfield will do all he can to reclaim the starting role, but Mayfield's perseverance in trying to play has given Keenum even more motivation to thrive and ensure he keeps the offense afloat.

"He's a tough, tough, tough dude," Keenum said. "He fought through some serious pain just to practice and get going. I can't speak on his injury, and I won't speak on it because I don't know much about it, but I do know he's tough. It'd take a freight train to keep him out of the game, and I'm assuming that's what it did because that dude plays through some serious pain. It's impressive to be around, and it's inspiring."