The Jets are preparing as if starting quarterback Sam Darnold will not available for at least a month, league sources said, without a firm timetable on precisely when he will be cleared after being diagnosed with mononucleosis this week.

The franchise was hoping for a breakthrough season from Darnold, their top pick in 2018, but his adjustment to a new scheme under new coach Adam Gase is being delayed indefinitely due to the illness. With mono being highly contagious, getting Darnold away from the facility and under proper care was the immediate priority.

Darnold was quickly ruled out for Monday and essentially Week 3 as well, with a bye looming in Week 4. There is no set return date at this point, I'm told. Mono can lead to the swelling of major organs, which are susceptible to rupturing playing a sport like football, and it is unknown how quickly his body will recovery and how long fatigue will be a factor. Weight loss is another concern, with eating normally often difficult due to swollen glands, a sore throat and loss of appetite.

The Jets are monitoring the situation closely, and providing Darnold the best care possible, but they could be going with Trevor Siemian as their starting quarterback well into October with it difficult to predict precisely how Darnold's body will respond.