CHARLOTTE — Derrick Brown's been rehabbing for months, riding an exercise bike, or walking on the zero-gravity treadmill during a lot of lonely months.

But when you see the look on his face this week, when he's out on the field with his teammates again after a painful 2024 (in many respects), you can tell the difference.

Brown's been among the majority of the roster here during the first week of voluntary offseason work, lifting and running as they prepare for what's next.

"I'm feeling good, man, feeling great, and excited to be back with the team and be back with the guys and moving around a little more," Brown said Wednesday. "Really, rehab kicked off, ... I was doing rehab two days after I had surgery, so it's been a long journey, but one that I won't let define me and, you know, just being able to get back on my feet probably the last two months of really building up strength to be able to attack the fieldwork."

Brown was lost for the season after a knee injury in the opener, and he said he's still unsure about the specific timing of the injury. As a guy used to playing most of the snaps (he played 89 percent of the total defensive snaps in 2023 or 940 total), he played his normal full load in the opener (60 snaps against the Saints) before realizing there was a significant problem.

"That's still a million-dollar question," he said of the timing of his injury. "Not sure when it happened; I really didn't start feeling anything until Monday morning. I thought it was going to be a little strange hit, or I got hit kind of funny, but it turned into a whole lot more than that. So, you know, I really didn't know what happened to me or how it happened, to be honest."

You could almost say the same thing about the defense that was left behind. Without their best player, things got sideways in a hurry, and they ended up setting an all-time record for points allowed.

"Losing Derrick, especially the first game of the season, that was a big blow for our defense," general manager Dan Morgan said. "I think, if you look around the NFL, if any team loses their best defender, it's a big-time impact and obviously it was a huge impact for us. We had just given him a big contract, and he's coming off a 100-tackle a year for a defensive tackle. So, we lost a lot of big plays, a lot of tackles when we lost him.

"And not only that, but on top of that, we lost his leadership. So getting him back is going to be huge."

Brown was around and on the sidelines late in the season (once he was able to be stable and protect himself in an unpredictable environment), so he was able to see the unraveling up close. They were last in the league in most categories (and allowed over 200 rushing yards in each of the last six games), so his eagerness to get back involves more than just his physical rehab.

"Man, we take it as a challenge," Brown said. "Nobody wants to finish last in defense in the NFL. It's not a very nice trophy to hang on the wall there, but it's one that, it is what it is.

"So now, I mean, we've got to go out there, we've got to execute, we've got to get back to doing what we do."

There was an intentional effort this offseason to add help, as they stepped into free agency with both feet, agreeing to deals with defensive linemen Tershawn Wharton and Bobby Brown III, outside linebacker Patrick Jones II, and safety Tre'von Moehrig on the first day of the negotiating period.

Coupled with nine draft picks this weekend (many of which are expected to help fortify that side of the ball), it will be a new look come the fall.

And since he's the guy in the middle of it all, Brown can't want to start making things right.

"We brought in a lot of great guys," Brown said. "I'm excited, you know. Especially missing last year and then being able to bring in guys right now, that's going to help us, help this team, and help this franchise.

"I'm excited to get going, that's for sure. Right now, everybody's running around in shorts and T-shirts, but I'm excited to get in the fire with those guys, build those relationships, and see where it goes from there."