Jets coach Adam Gase announced Darnold's game status Thursday. Gase said he found out about Darnold's mono Wednesday night. He also said Darnold could be out for multiple weeks. Darnold is still going through tests after the diagnosis.
Gase said Darnold will be resting as part of his recovery. The Jets quarterback has lost weight over the last week as a result of the disease.
"No. 14 has mono and will be out for this game," Gase told reporters. "So Trevor Siemian will be starting. Luke Falk will get elevated at some point and be the backup."
Jets running back Le'Veon Bell is also dealing with a shoulder injury and missed Thursday's practice. C.J. Mosley, Quinnen Williams, John-Franklin Myers and Demaryius Thomas also missed Thursday's session. Bell is having an MRI Thursday. Gase said Bell's injury could just be soreness.
Darnold completed 28 of 41 passes for 17 yards and a touchdown in the Jets' Week 1 loss to the Buffalo Bills. Siemian completed 59 percent of his passes for 2,285 yards, 12 touchdowns and 14 interceptions in 11 games in 2017 for the Denver Broncos. He has a 13-11 record in 24 career starts.
"Nothing really crazy [changes] for us," Gase said when asked about the game plan against the Browns. "The way we have it built, it's really flexible where Trevor is good."
The Jets host the Browns at 8:15 p.m. EDT Monday at MetLife Stadium in East Rutherford, N.J. They have a Week 4 bye this season, before returning to action against the Philadelphia Eagles on Oct. 6 in Philadelphia.