Don’t expect to see Sam Darnold for a while.

That is the opinion of Dr. David Chao, the former Chargers team physician who operates the website profootballdoc.com, after the Jets quarterback was diagnosed with mononucleosis.

“He’s going to miss a lot of time,” Chao said Thursday. “This isn’t just about how does he feel. It’s about more than that.”

The Jets have ruled Darnold out for Monday’s game against the Browns, and coach Adam Gase acknowledged the quarterback could miss several weeks. Chao said the timeline starts at four to six weeks for Darnold.

Chao specified the Jets will have three major issues to worry about with Darnold’s diagnosis. First, mono typically causes the spleen and/or liver to enlarge. Someone cannot have any physical contact because of the risk of rupturing the organs. Second, Darnold will feel tired, have a general malaise and will lose weight. That could last for multiple weeks. Finally, the Jets can’t risk Darnold even being around the team because he could infect others.

Chao, who worked for the Chargers for 17 years, said you can forget about Darnold playing in September and he may not even be able to return in early October.

“This is a big deal,” Chao said. “With this diagnosis of mono, an injured-reserve stint is not off the table. I’m not saying he’s going on injured reserve but this starts at four to six weeks. Any four-to-six-week injury puts IR in the conversation.”

Chao emphasized he is not predicting Darnold will end up on IR, but merely saying it can’t be ruled out.

The Jets will start Trevor Siemian in his place in Monday’s game.