Chicago Bears quarterback Justin Fields, who is dealing with a separated left shoulder with partially torn ligaments, is not expected to play Sunday at the New York Jets, a source told ESPN's Adam Schefter.

The Bears are expected to start Trevor Siemian at quarterback, and the team also promoted Nathan Peterman from the practice squad Saturday to serve as the backup at that position.

Chicago Bears quarterback Justin Fields said Wednesday that he is dealing with an injury to the acromioclavicular joint in his left shoulder and will evaluate how he feels later this week before determining whether he'll play against the New York Jets.

"It's a separated shoulder with partially torn ligaments," Fields said, describing his injury. "Basically, like an AC joint. That's my understanding of it."

Justin Fields injured his left (non-throwing) shoulder in the final moments of the Chicago Bears' 27-24 loss to the Atlanta Falcons on Sunday.

Fields suffered the injury on the first play of the Bears' last drive when he rushed toward Chicago's sideline for a 1-yard gain on a designed run. 

The quarterback landed hard on his left shoulder out of bounds after he was tackled and was slow to get up. Fields took another hit moments later on another run play when Grady Jarrett hit him with his helmet as Fields was sliding.

Following the loss, Fields was carted back to the Bears locker room, where he received an X-ray and IV treatment. During his postgame news conference, Fields was not wearing a sling and said he did not know the extent of his injury.

Justin Fields continued to make his case as the top quarterback from the 2021 draft class after reaching historic heights during Chicago's 35-32 loss to the Miami Dolphins.

The Bears quarterback set multiple NFL and franchise records on Sunday. His 178 rushing yards are the most by a quarterback in a regular-season game in the Super Bowl era, surpassing the previous high set by former Falcons quarterback Michael Vick (173) in 2002.