BEREA — The Browns won’t face starting quarterback Sam Darnold when they visit the New York Jets for "Monday Night Football."

Darnold will sit out because he has mononucleosis, Jets coach Adam Gase announced Thursday during a news conference. Gase explained the Jets thought Darnold had strep throat until they found out late Wednesday night it's mono. Gase said it looks like Darnold will miss more than one game, and he informed the rest of the team Thursday morning.

"Unfortunate news for Sam," Browns quarterback Baker Mayfield said. "I hope he gets healthy. I've never had [mono] — knock on wood — but I know it's not a fun process just laying around and not able to do anything."

"A very unfortunate situation," Browns free safety Damarious Randall said. "You never want to have any time of sickness or anything like that. I wish the best for him. Definitely getting prepared for the next man up and looking forward to it."

Gase said backup quarterback Trevor Siemian will start against the Browns, and the Jets will promote Luke Falk from their practice squad to serve as their No. 2 QB.

Coach Freddie Kitchens insisted Darnold being shut down won't change how the Browns (0-1) get ready for the Jets (0-1).

"It was very evident [in Sunday's 43-13 loss to the Tennessee Titans], we don't need to worry about who's playing, who's not playing," Kitchens said. "We're going to prepare like we prepare.

"Nothing at all [will change]. We’re going to be focused on our preparation during the week the same as we would’ve been before. We’re going to try to get after the quarterback just like we did before. We try to affect the quarterback every way that we can, through coverage, through pressure."

Gase said his game plan won't be altered much, either.

"Nothing really crazy for us," Gase said. "The way we have it built, it’s really flexible to where Trevor is good. We thought [Darnold] was sick [Wednesday]. They ran more tests. So with Trevor being able to practice [with the starters Wednesday], that’ll help us."

The third overall pick in last year's draft, Darnold is 4-10 as an NFL starter. He has completed 58.7 percent of his passes for 3,040 yards with 18 touchdowns and 15 interceptions. His career passer rating is 78.3, and he has taken 34 sacks.

A seventh-round pick in 2015, Siemian is 13-11 as an NFL starter. He has completed 59.3 percent of his passes for 5,686 yards with 30 touchdowns and 24 interceptions. His career passer rating is 79.9, and he has taken 64 sacks.

"These [backup quarterbacks] are in the NFL for a reason," Kitchens said. "Trevor can play. All right? Nothing’s changed.

"I know he makes NFL throws. ... He’s a good player."

Other injury updates

Jets starting running back Le’Veon Bell sat out Thursday’s practice with a shoulder injury and had an MRI, Gase said. ESPN reported the MRI did not reveal any major damage or tears.

"I got great news, my shoulder is fine so no worries," Bell tweeted Thursday evening. "Just had to make sure everything was ready to go for Monday night."

Linebacker C.J. Mosley (groin), defensive linemen Quinnen Williams (ankle) and John-Franklin Myers (foot), left tackle Kelvin Beachum (ankle) and wide receiver Demaryius Thomas (hamstring) are the other Jets players who were sidelined Thursday.

For the Browns, Randall (stomach virus) returned to practice Thursday after missing Tuesday's session. Defensive end Chris Smith (personal), offensive tackle Kendall Lamm (knee), linebacker Adarius Taylor (high-ankle sprain) and running back Dontrell Hilliard (concussion) remained idle. Receiver Rashard Higgins (knee), left guard Joel Bitonio (abdomen) were limited participants.

Mayfield was not listed Thursday on the Browns' first injury report of the week. Asked about hurting his right wrist against the Titans, Mayfield held his throwing arm up and said, "It looks good."

Roster moves

The Browns signed guard Colby Gossett to the practice squad and released rookie cornerback Donnie Lewis Jr. from the practice squad.

A sixth-round pick of the Minnesota Vikings last year, Gossett appeared in five games, with four starts, for the Arizona Cardinals. He was a member of the New England Patriots' practice squad in Week 1 of this season.

The Browns drafted Lewis in the seventh round this year.

Nate Ulrich can be reached at nulrich@thebeaconjournal.com. Read his Browns coverage at www.ohio.com/browns. Follow him on Twitter at www.twitter.com/ByNateUlrich and on Facebook www.facebook.com/abj.sports.