Panthers defensive tackle Andre Neblett said his positive test for a banned performance-enhancing substance was caused by an over-the-counter dietary supplement.

Neblett unsuccessfully appealed the four-game suspension that accompanies a first violation of the league’s performance-enhancing substance policy.

Neblett did not identify the supplement, which he said he was taking to keep his weight down. The 6-foot Neblett is listed at 310 pounds on the Panthers’ current roster, 15 pounds heavier than last season.

“(It was) something I know I shouldn’t have took and should have checked with my trainer,” Neblett said Tuesday.

Neblett, a third-year player who started four games last season after starters Sione Fua and Terrell McClain were injured, said he let his family and team down.

“I’m costing a team that can potentially make it to the playoffs four games, and I can be a guy that can help,” he said.

Neblett can practice and play in games throughout the preseason. Panthers coach Ron Rivera said Neblett would be evaluated like any other player.

But Neblett, who had shoulder surgery in the offseason, said his suspension would make it harder to make the team.

“I’m not going to be there for four games. So that means somebody’s going to be able to step up and take that spot, just as I did,” Neblett said. “So it’s definitely going to be some work getting back.”

BACK IN ACTION: This week’s rookie camp also features the team’s three quarterbacks and players returning from injuries, with the majority on the defensive side.

Defensive tackle Ron Edwards, who tore his triceps during his first training camp practice last year, was glad to get back.

“Just being on the field and putting your hand in the dirt, that’s just what I do,” Edwards said. “Just being without it does something to me. I’m really enjoying getting back into it.”

Linebackers Thomas Davis (knee) and Jon Beason (Achilles) and defensive end Charles Johnson (knee) also practiced Tuesday, the second of three scheduled sessions.

Johnson, who had arthroscopic surgery to clean up his right knee, said he remains less than 100 percent but expects to practice when training camp opens this weekend.

“I’m ready for training camp to start, and I’m ready for training camp to end,” Johnson joked.

Davis, trying to come back from a third ACL surgery on his right knee, said he might be one of the few veterans fired up about camp.

“With my situation and the way things have gone, I’m definitely excited to make that drive down 85 to Spartanburg,” Davis said. “I’m taking this opportunity and I’m looking ahead. Everything that has happened in the past is strictly that – in the past. I’m looking forward to the future. I’m looking forward to bright things.”

SHOCKEY VALUE: Free agent tight end Jeremy Shockey, who spent last year with the Panthers, was scheduled to visit the Philadelphia Eagles this week.

But that was put on hold after the Eagles worked out former Minnesota Vikings tight end Visanthe Shiancoe, according to the Philadelphia Inquirer.

The Panthers have not ruled out bringing Shockey back to pair with starter Greg Olsen. But first they want to look at Gary Barnidge, who was in the midst of a strong camp last year before breaking his ankle.

Shockey caught 37 passes for 455 yards and four touchdowns last season.

EXTRA POINTS: Rivera said incumbent Byron Bell would get the first-team reps at right tackle following Monday’s trade that sent Jeff Otah to the Jets for a conditional, seventh-round pick. Rivera said Otah, who missed 31 of his last 35 games because of injuries, could benefit from the change.

“It’s tough. You get injured and you get injured again, and you get a little bit stale. I think sometimes a change of venue helps good football players,” Rivera said.

“When he went down last year and we put him on IR, for 10 weeks he worked pretty doggone hard. I think the thing people have to understand is sometimes nagging injuries are just that – they nag and they bother.”

• In a precautionary move, the Panthers placed wideout David Gettis on the physically unable to perform list. Gettis is almost a year removed from ACL surgery, but he tweaked his hamstring recently and the team wanted to give him some extra time to recover.

Players can come off the PUP list any time during the preseason, but must sit out six games if they begin the regular season on it.