The Jets are signing QB David Fales to back up Luke Falk, a source confirmed to SNY's Ralph Vacchiano.
Fales played under head coach Adam Gase when the Jets' head coach was with the Dolphins.
The 28-year-old Fales has not played a regular season NFL game since 2017, when he played two games for the Dolphins -- completing 29 of 43 passes for 265 yards with one touchdown and one interception.
Before joining the Dolphins, Fales was with the Bears, where he appeared in one game in 2016.
Gase said on Tuesday that the team -- in the wake of Trevor Siemian's season-ending ankle injury -- was not looking for someone to fill in for Darnold while he remains out with mono. Instead, they were looking for a backup for Falk, which they've seemingly found with Fales.
Darnold has already missed Week 2 due to his illness and will also be inactive for Week 3, but he returned to the Jets' facility on Tuesday for the first time since being diagnosed and said later on Tuesday that he was feeling better and targeting Week 5 for his return.
"It sucks but it is what it is," Darnold said during an appearance on The Michael Kay Show. "I knew I couldn't do anything about it. I've just got to let it run its course and do everything I could to get better. Right after I heard the news I just started pounding Vitamin C and doing all of the little things that I could to try to get better."