Stephen A. Smith reacts to the news that Sam Darnold is now expected to miss multiple weeks with mononucleosis. (1:19)

Stephen A.: For all intents and purposes, the Jets' season is over (1:19)

FLORHAM PARK, N.J. -- The macro view of the Sam Darnold bombshell is that it's another bad-luck blow for one of the most star-crossed franchises in sports, the New York Jets. Darnold, sidelined indefinitely with mononucleosis, was -- is -- the one who's supposed to change all that.

The micro perspective is the Jets (0-1) have to figure out a way to save their season with Trevor Siemian at quarterback. For many reasons, it will be difficult.

Lowest Total QBR Since 2016 QBR among 30 QBs with at least 1,000 action plays since the start of 2016: QBR Trevor Siemian 42.1 Brock Osweiler 46.1 Eli Manning 47.0 Blake Bortles 48.6 Source: ESPN Stats & Info | QBR explained

Siemian's résumé includes a 13-11 record, which coach Adam Gase mentioned to the team Thursday morning when he broke the Darnold news, but the former Denver Broncos starter hasn't played a regular-season game since Dec. 14, 2017. He was Kirk Cousins' caddie last season with the Minnesota Vikings, a fixture on the bench.

Now he's being asked to rescue the Jets in what probably will be a multigame gig against a brutal schedule. He will start Monday against the Cleveland Browns (8:15 p.m. ET, ESPN), followed by at the New England Patriots, the Week 4 bye, at the Philadelphia Eagles, at home against the Dallas Cowboys and the Patriots (again).

That would have been difficult for a healthy Darnold. It is a massive challenge for Siemian, who has the worst Total QBR (42.1) among the 30 quarterbacks with at least 1,000 action plays since 2016. Luke Falk, who will be elevated from the practice squad, will serve as the No. 2 QB on Monday night.

The early bye will help, but the Jets could be 0-3 at that point. Monday night will be a huge game for the Jets -- as big as it gets for mid-September.

Siemian was uneven in training camp, impressing with his strong arm on some days but struggling with accuracy on others. His preseason numbers look good on paper (25-for-32, one touchdown, no interceptions), but he passed for 158 yards. He was Captain Checkdown against second- and third-string defenses.

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Gase will have to tweak his game plans. Unlike Darnold, whose strength is having the ability to make plays outside the pocket, Siemian is a pure pocket passer. When his protection breaks down, he won't be able to make improvisational plays the way Darnold can. When his protections hold up, he has the potential to carve up a defense. The Jets know this first hand. In 2017, Siemian completed 19 of 31 passes for 200 yards and a touchdown in a 23-0 win against the Jets.

The Jets signed Siemian to a one-year, $2 million contract because they felt confident he could be a short-term starter.

"He's not a panic guy," Gase said. "He's got a calmness about him."

Siemian would be calmer with Le'Veon Bell in the backfield, but there's some question about that. Bell, dealing with shoulder soreness, was scheduled for an MRI on Thursday afternoon. Gase didn't seem alarmed, but players don't have MRIs unless there's some concern. If Bell is full-go for Monday night, he can be the workhorse, taking the pressure off Siemian. The offense needs to run through him because he's the best player. If Bell is out, Ty Montgomery and Bilal Powell will pick up the workload.

Siemian won't have starting wide receiver Quincy Enunwa (season-ending neck injury) and the offensive line, which struggled in the Jets' Week 1 loss to Buffalo, is a work in progress. Center Ryan Kalil, who came out of retirement at the start of training camp, spent the entire summer practicing with Darnold. Now he has to get familiar with a new quarterback while continuing to learn the nuances of Gase's offense.

Basically, the Jets are a mess on offense.

A silver lining? Gase is no stranger to quarterback calamities. In 2017, he lost Ryan Tannehill in training camp to a season-ending knee injury, prompting the Miami Dolphins to coax Jay Cutler off his couch. That didn't go well, but Gase learned how to cope with adversity.

"What's our attitude going to be?" Gase asked rhetorically. "Is it going to be woe is me, the sky is falling? Or is this something we're going to embrace?

"We're going to look back at this and this is going to be a good thing for us," he added. "I think it's going to bring the locker room even tighter."

The morale will be tested, no doubt.