Darnold has not played since Week 1 after being diagnosed with mononucleosis on Sept. 12.
He was not cleared to play after undergoing testing Thursday night, Gase said. Darnold was set to have an ultrasound and a blood test to determine if his spleen, previously enlarged, has returned to its normal size.
An enlarged spleen — a common symptom of mono — could rupture with a blow to the midsection. Darnold has been practicing with a custom-made, hard-plastic brace that protects his rib-cage area and he’s planning to wear the brace when he plays.
Darnold had said he felt good enough to play but wouldn’t risk his long-term health.
“It’s a tough thing because you want to stay safe,” Darnold said Thursday. “I want to make sure that I’m safe out there and I’m not going to die.”
The Jets (0-3), coming off their bye week, are desperate for a spark. The offense has generated only one touchdown, having gone 29 straight possessions without reaching the end zone. They have started three different quarterbacks — Darnold, Trevor Siemian and Falk. Siemian suffered a season-ending ankle injury in his first game.
ESPN’s Rich Cimini contributed to this report.