Sam Darnold returned to the Jets’ practice facility on Tuesday. He watched practice on Wednesday. He’s feeling “way better.”

But until his spleen, enlarged as he deals with mononucleosis, shrinks back to its normal condition, he can’t play. He would be at the risk of rupturing his spleen.

“I know the spleen is the main issue,” the second-year quarterback said.

Darnold has yet to be cleared for physical activity. The plan is for him to begin running next week after getting a checkup on Monday. Then he can really work on getting back onto the field and being under center for the Jets’ game Week 5 at Philadelphia, following their bye week.

“I have full confidence that I’ll be ready for the Eagles games,” said Darnold, who doesn’t believe he will travel to Sunday’s game against the Patriots.

“I’m going to do what it takes to get ready. Whatever that takes, I’m going to do it and do it to the best of my ability.” Darnold wouldn’t guarantee he would play then, admitting there could be setbacks, but that’s the game he has set as his goal for a return. So have his doctors. They believe it is realistic.

“I feel way better, way better today,” Darnold said. “My energy is up. Not exactly where I would like it to be by next week and other weeks as well. But it’s been good. It’s been pretty good, all things considered.”

Luke Falk, who began the season as the third-string quarterback, will start Sunday against the Patriots after Trevor Siemian was lost for the season due to a severe left ankle injury. The Jets, on Wednesday, signed David Fales, who played for coach Adam Gase with the Dolphins, to back up Falk.

After an impressive summer, Darnold struggled in the regular season opener. He wasn’t feeling well then, but kept it to himself. A few days later, it was diagnosed as mono.

But he’s feeling better now, his energy has improved — and so have his spirits. Soon, he will be back at quarterback for the Jets. Possibly on Oct. 6 against the Eagles.

“I’m hoping to come back stronger than I was. Because that first game I wasn’t myself, I wasn’t playing like myself,” Darnold said. “I felt a little bit more uncomfortable than I had in the preseason and training camp. So just looking to come back strong, come back knowing the offense that much more and playing well.”