PHILADELPHIA (973espn.com) - Slim probably turned to none for the New York Jets Friday when Sam Darnold was ruled out of Sunday's game with the Eagles at Lincoln Financial Field.

The Jets' second-year quarterback, who felt "good to go" on Thursday, was not cleared by doctors after his latest tests revealed an enlarged spleen, an effect from his recent bout with mononucleosis.

The thought around the league was that if the spleen wasn't an issue conditioning would be and Darnold remained a long-shot to play but Jets coach Adam Gase gave the 2018 No. 3 overall pick the vast majority of the first-team reps on Wednesday and Thursday, leaving Luke Falk in a precarious position against a Philadelphia defense which should be ripe for the picking down a host of cornerbacks.

"The labs didn't come back the way we were hoping," Gase explained. "I know Sam is disappointed, but we'll be able to adjust and work quickly."

Falk, Gardner Minshew's predecessor at Washington State, learned he would be starting on Thursday night and was able to take the first-team work on Friday, a lesser practice day in the NFL.

This will be the Jets' third straight game without Darnold, who played the season opener ill and was diagnosed with mono two days later. Veteran Trevor Siemian started Week 2, but he suffered a season-ending ankle injury and Falk was up in Week 3. David Fales was signed to serve as Falk's backup against the Eagles.

"He tried to do everything he could," Gase said of Darnold. "He did everything he was asked to do. He did everything the doctors told him to do. It just didn't work out for him."

With all the issues at QB, the Jets' offense has been the worst in the NFL, producing just one touchdown in three games. Falk has led 21 consecutive drives without points entering Sunday.

The Eagles, meanwhile, are so light at CB that Ryan Lewis was elevated from the practice squad on Friday with tight end Alex Ellis being waived/injured to make room.

Jim Schwartz has only three healthy corners -- Rasul Douglas, the recently-re-signed Orlando Scandrick, and Craig James. Sidney Jones is listed as questionable Sunday with a hamstring issue and is expected to play although how much is certainly up for debate. Ronald Darby (hamstring) and Avonte Maddox (neck/concussion) were officially ruled out for the Jets while Jalen Mills remains on the PUP list and Cre'Von LeBlanc on injured reserve, both with foot injuries.

As for what Gase is thinking the Eagles might have an advantage due to the presence of defensive special assistant Matt Burke, who was Gase's defensive coordinator in Miami.

"He has a little understanding probably of how Adam thinks," Eagles coach Doug Pederson admitted. "Matt has been a great addition to Jim [Schwartz] on the defensive side, being another set of eyes on defense, being that he's been a coordinator, he's a young coordinator, obviously, but he doesn't have a position to coach, so he can really dive into our defense and find ways of improving that as he sees fit, and he and Jim have obviously worked together.

"But understanding Adam, I think he can maybe think situationally a little bit, how Adam thinks in certain areas of the field and maybe relay some of that to Jim."

-John McMullen covers the Eagles and the NFL for 973espn.com. You can reach him at jmcmullen44@gmail.com or on Twitter @JFMcMullen