RALEIGH — Tom O'Brien added linebacker Terrell Manning's name to his list of players missing on N.C. State's defense.

The Wolfpack coach rattled off the names of injured players Monday and concluded: "It has been a difficult year to play defense around here."

Manning, the Wolfpack's starting weakside linebacker, had surgery on his left knee on Monday and will miss Thursday's game at Cincinnati (8 p.m., ESPN). His status will be re-evaluated going forward, O'Brien said, but Manning's injury removes one of the most dynamic players from a Wolfpack defense that has struggled for the better part of the first three games.

Manning joins defensive tackles J.R. Sweezy and Thomas Teal (both out with a fractured foot) on the weekly injured list. Cornerback Jarvis Byrd (knee) and reserve linebacker Sterling Lucas (knee) are already out for the season.

One of N.C. State's starting defensive ends, senior Jeff Rieskamp, missed the past two games with a shoulder injury, but O'Brien expects him to return for Thursday's road trip to a Big East foe.

"Anybody coming back would be a big boost," O'Brien said.

Injuries, both in significance and volume, marked O'Brien's first three seasons in Raleigh and kept the program under .500. With relative health across the board, the Wolfpack surged to 9-4 last year.

The loss of Sweezy, the team's top defensive lineman, was difficult to withstand. The loss of Manning, who had five sacks last year, will cripple the Pack further.

"So far, I've been here for five years, and we've had pretty much bad luck with injuries," senior defensive tackle Markus Kuhn said. "I guess this year is the year for the defense, where it hit all of us."

Manning left Saturday's 35-13 win over South Alabama with 2:22 left in the first quarter. After being treated on the field, he jogged off the field but did not return.

He was at State's practice Monday morning, wearing shorts, before the scheduled surgery.

In Maddox's absence Saturday night against USA, senior Dwayne Maddox filled in and finished with eight tackles. Maddox started 11 times in 2009 and four in 2008. He had 11 tackles for a loss last season, excelling in linebackers coach Jon Tenuta's blitzing schemes.

"At least Dwayne Maddox has some experience and he's been around," O'Brien said. "He's going to have to step up and make some plays now."

Note: N.C. State's home game against Georgia Tech on Oct. 1 will start at 3:30 p.m. and will be televised regionally by ABC.

jp.giglio@newsobserver.com or 919-829-8938