Jets QB Sam Darnold out vs. Browns with Mono; Trevor Siemian to Start on MNF

Scott Polacek @@ScottPolacekFeatured ColumnistSeptember 12, 2019

FILE - In this Sunday, Nov. 4, 2018, file photo, New York Jets quarterback Sam Darnold (14) walks off the field after an NFL football game in Miami Gardens, Fla. Darnold has a boot on his right foot and is not practicing, leaving his status for the team's game against Buffalo on Sunday in doubt. Darnold was injured during the Jets' 13-6 loss at Miami last Sunday, but finished the game. (AP Photo/Lynne Sladky, FIle)

Lynne Sladky/Associated Press

New York Jets head coach Adam Gase announced Thursday that quarterback Sam Darnold will miss Monday night's home game against the Cleveland Browns with mono and will be out indefinitely.

Gase added that Trevor Siemian will get the start under center, with Luke Falk serving as the backup:

SNY @SNYtv
Sam Darnold has mono and will miss Monday's game against the Browns, per Adam Gase. https://t.co/b3rUSCVFNM

Dennis Waszak Jr. @DWAZ73
Gase says Darnold's biggest concern is weight loss. Coach says he has already lost about 5 pounds or so. #Jets

This isn't the first injury- or illness-related setback for the 22-year-old Darnold, as he missed time with a foot injury that left him in a walking boot during his rookie season.

The Jets blew a 16-point lead in a season-opening loss to the Buffalo Bills last week, though Darnold had a decent game, completing 68.3 percent of his passes for 175 yards and one touchdown.

In Siemian, the Jets have a solid backup with starting experience. The Northwestern product played 11 games in 2017 and 14 games in 2016 for the Denver Broncos and entered the 2019 campaign with 30 touchdown throws and 24 picks.

He is 13-11 as a starter.