As one key defensive player returned Wednesday for the Carolina Panthers, another was relegated to observer status.

Defensive tackle Star Lotulelei practiced for the first time in six weeks while linebacker Luke Kuechly could only watch his teammates get ready for Sunday's home opener against the Texans.

Kuechly, who sustained a concussion late in the first half of Week 1's win in Jacksonville, is in the NFL’s concussion protocol. It’s impossible to predict if he’ll be cleared to play in four days.

"He's in the protocol, that's all I can tell you," coach Ron Rivera said. “No conjecture would be fair because, again, this is serious and we’ve just got to follow the protocol. I don’t want to put anything out there that’s not right or not true.

"To guess or to assume would be unfair."

Kuechly, wearing a blue practice jersey but no pads, walked into practice shortly after it began with head trainer Ryan Vermillion. The two-time Pro Bowler stretched with the team and then followed around the linebackers during drills.

Rivera didn't know where Kuechly is in the protocol, but he did pop in the film and weight rooms.

"He was trying to do more than he was supposed to and [Vermillion] had to tell him, 'No, just settle down.' That's just him," Rivera said.

During his three years at Boston College and through 3-plus seasons as a pro, Kuechly has never missed a game.

Before his early exit Sunday, he had played 93 percent of potential snaps since coming to Carolina in 2012. That number included 130 missed snaps during the first four games of his career when he was the Panthers' third linebacker. After moved to middle linebacker, Kueckly missed just 63 plays over his next 44 games.

Rivera said even if Kuechly is cleared by Sunday, that doesn't guarantee he'll play. But if he's not on the field before then, that doesn't mean he won't.

"Luke doesn't need to practice, I'll promise you that much right now. He's a smart football player. He understands the game; he knows the game," Rivera said. "To be able to play effectively, to play to his ability, he probably doesn't need to practice."

For Lotulelei, practice was a welcome addition to a regimen that was mostly limited to an exercise bike the past few weeks.

The last time he was on the field, he took a cart right off of it in Spartanburg. A stress reaction in his surgically repaired foot forced him to miss the entire preseason and last week's opener.

Before that game, Lotulelei said, “We’ve got to get through this, got to make sure it’s 100 percent before I come back because it’s a long season.”

A week later, he wouldn't speculate on if he'll be in the lineup against the Texans, but the itch to get back out there sounded stronger.

"When I come back I don't think it'll be at 100 percent," Lotulelei said Wednesday. "But it'll be good enough to be out there."