The Indianapolis Colts are in wait-and-see mode when it comes to the availability of their All-Pro linebacker heading into a short week.

Shaquille Leonard exited Sunday's Week 4 loss to the Tennessee Titans due to a concussion, putting his status into question for Thursday night's road question against the Denver Broncos.

"Shaq, as you saw, had the concussion. He's in the protocol," Colts head coach Frank Reich told reporters after Sunday's game. "Don't know the extent of it yet. We'll see as we go there."

Leonard's injury was a tough break for the three-time All-Pro, who was making his 2022 season debut on Sunday after undergoing offseason back surgery.

Reich had confirmed before the game that Leonard would be on a "pitch count" for his first start, yet he had still racked up a couple tackles by the time he suffered his injury about midway through the second quarter, colliding with teammate Zaire Franklin near the goal line as the Titans' Chig Okonkwo found the end zone for an eight-yard touchdown reception.

Leonard, who walked to the locker room with the help of trainers, was initially being evaluated for a head injury before the team confirmed he was being ruled out for the rest of the game with a concussion.

"I'm playing off, I got my eyes on the QB. He got a tough play on the goal line, it's on the 1-yard line. I threw everything I had in it and missed my target a little bit, unfortunately," Franklin said of the play. "That's a part of the game. I do feel terrible that I was the one that hit him. But he's a tough dude so I know he'll be ready to bounce back."

"It sucks seeing somebody go down and having to get off the field and not return," Colts defensive tackle DeForest Buckner said. "Obviously you're concerned for that guy, whoever it is. It just sucks, especially that it was Shaq, his debut got cut short."

Players who enter the concussion protocol typically face a steep uphill climb when it comes to their availability on short weeks. Another potential factor at play could be expected changes in the coming days to the league's concussion protocol that were announced in a joint statement by the NFL and NFLPA on Saturday night.

The Colts had been utilizing Franklin, Bobby Okereke and E.J. Speed at linebacker in Leonard's absence the first three weeks of the season — a lineup they could revisit should be unavailable Thursday night in Denver. Franklin on Sunday had a career-best 15 tackles, while Okereke added eight and Speed had three total stops.

"I talked to him at halftime, I'll call him tonight after we watch the film," Franklin said of Leonard. "That's my brother, so (I) always want the best for him, always pulling for him and help him any way I can."