ALLEN PARK, Mich. (AP) -- DeAndre Levy's status remains unclear for Detroit's season opener.

Levy was not participating during the portion of practice open to reporters Monday, and coach Jim Caldwell was noncommittal about his chances of playing in Sunday's game at San Diego.

"Not certain," Caldwell said. "He's not out there today, there's no guarantee."

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Caldwell would not discuss the particulars of what's been keeping Levy out of action, saying an injury report would be due Wednesday. The linebacker's status has been in doubt for a while. He did not play in either of Detroit's final two preseason games.

Defensive tackle Caraun Reid and guard Larry Warford, both of whom have been dealing with ankle injuries, were also helmetless at practice.

The Lions put rookie cornerback Alex Carter on injured reserve-designated to return. They also re-signed defensive tackle Jermelle Cudjo, who was cut over the weekend, and signed cornerback Stanley Jean-Baptiste to the practice squad.

Levy's fine performance in 2014 was a big reason the Lions had one of the league's best defenses, and with his contract set to expire after this season, Detroit was able to secure his services with a four-year extension last month.

He might be an even more crucial player this season after the Lions lost defensive tackles Ndamukong Suh and Nick Fairley to free agency.

The Lions can feel a bit better about two other key players who have dealt with injury problems this preseason. Defensive tackle Haloti Ngata and running back Joique Bell were on the practice field Monday.

"With Joique being back, obviously he adds a little bit more experience to the group. ... He's a tough runner, he looks good and can perform well," Caldwell said. "Obviously, Haloti is an integral part of what we think we're going to be able to do up front."

NOTES: General manager Martin Mayhew made a rare appearance to talk to reporters after practice Monday. "I'm going to apologize in advance for not saying anything controversial or remotely interesting," he said. Mayhew talked a bit about TE Joseph Fauria, who was cut over the weekend. Fauria caught seven TD passes as a rookie in 2013, but he played only seven games during an injury-shortened 2014. "It's the meritocracy," Mayhew said. "I think you've got to perform at a high level, consistently, all the time. Some people say that the best ability is availability."