C.J. Mosley is back, but what percentage the Jets middle linebacker is back at for Sunday's game at Jacksonville is yet to be determined.

"The doctors are doing a really deep dive, trying to figure out where things are coming from," head coach Adam Gase said before today's first practice of the week for the Jaguars, which Mosley sat out. "It might just be more than a groin. We're just trying to figure all that stuff out."

Gase said his and the medical staff's caution stemmed from what he saw of Mosley in his return to action against the Patriots after missing Games 2-5 with a groin injury suffered in the opener against the Bills. Mosley played 68 mostly quiet defensive snaps (three assisted tackles) before exiting the Monday night game early in the fourth quarter.

"It seemed like every time he was on the ground, he'd get up and he just didn't seem comfortable," Gase said. "I was glad they pulled him out when they did. I didn't know what was wrong with him. All indications going into the game were that he felt really good. Especially watching in practice, I saw him look like the guy before the Buffalo game. And I don't know what changed there. I didn't know if he got hit, if he opened up and something wasn't right. Nobody said anything. I don't think he was saying anything to anybody."

Mosley didn't speak with reporters Wednesday. Early Tuesday morning in the Jets' MetLife Stadium locker room, he said he felt the groin a little bit but just played through it. Asked if he aggravated the injury during the previous week of practice, he was definitive.

"Nah. If I had aggravated it, I probably wouldn't have played," he said. "I aggravated it the first game and couldn't finish. So the positive note is I did finish this game until the coaches took me out."

It's hard to say this early in the week what's ahead for the Jets defense vs. the 3-4 Jaguars, who've begun the season surprisingly well with RB Leonard Fournette leading the run game and rookie Gardner Minshew stepping in for injured QB Nick Foles in the Jags' opener and keeping the offense moving.

On the one hand, Gase said the Jets could be getting an inside 'backer back in action with Neville Hewitt limited at practice after neck and knee injuries kept him out vs. the Patriots. But on the other hand, LB Albert McClellan remains in the concussion protocol.

"Anytime he's not out at practice, it's not ideal," the coach said. "Not only is he one of our better players, but he's a captain, and we're thin right now, running out of bodies at linebacker."

Yet there are no signs yet that the team's doctors and trainers will come out of their deep dive recommending that Mosley be closed down a while longer.

And Mosley is all about football. As Gase said, "He's always going to push to practice." And as Mosley said after the game:

"It's a groin injury, which affects every move that I make at my position. So unless I don't play a lot, that's the only way it's not going to get better. And that's not really in my plans, not to play the rest of the season."