Lions head coach Dan Campbell confirmed Wednesday that safety C.J. Gardner-Johnson will have surgery on the torn pectoral muscle he suffered in Sunday's loss to Seattle which will keep him sidelined indefinitely.

Campbell referred to Gardner-Johnson's injury as a 'clean' tear which is normally good for surgery, and he thinks there's a chance Gardner-Johnson could return to the field near the end of the season.

Now the Lions will turn to Tracy Walker to be a starter on their defense again.

"Yeah, it's very valuable. We're fortunate to have depth in a number of areas and that's of them is at that position there," Campbell said of having a backup like Walker, who's played in 64 career games with 37 starts and has been a captain on defense for this team.

"Having a guy like Tracy who's got time on task, somebody we've got a lot of faith in, trust in, that alleviates a lot of pressure and stress for us because we know he's game ready, he's been in it. He's taken on a big role now and we have a ton of faith in Trace, so he's another guy I'm glad he's here with us."

Walker admitted it was hard to lose his starting job this season, but he was very professional about it. Campbell said weeks ago there was going to be a time when the team needed Walker to step up, and it just so happens to be the anniversary weekend of the lowest point in his career.

"I just look at it like a great opportunity for me to come back considering I'm coming back from my injury," Walker said Wednesday. "It's a special week for me considering same week I tore my Achilles. It's such a blessing for me and I'm looking at it like I have to capitalize on the opportunity right now."

Walker said he'll be pretty emotional Sunday coming out of the tunnel when the defensive starters are introduced.

"Great spot to be in and I'm very blessed," Walker said.

RUN DEFENSE CHALLENGED

The Lions have done a pretty good job through the first two weeks of the season defending the run. They rank ninth, allowing on average 86.0 yards per game.

Those numbers will certainly be tested this week.

Atlanta comes into Sunday's contest averaging 170.5 yards per game on the ground, fourth best in the league, and they rank second in the NFL with 11 runs of 10-or-more yards. Only Cleveland (13) has more.

Rookie Bijan Robinson rushed for a career-high 124 yards in the Falcons' win over Green Bay last week and also caught four passes for 48 yards.

Second-year back Tyler Allgeier rushed for 1,000 yards as a rookie and is a physical, tough, power runner.

"This No. 7 (Robinson) is an elusive back," Campbell said Wednesday. "Looks like a power back but he's really got excellent feet. You give him a lane and give him space and that's where he's really dangerous.

"Then they bring in Allgeier and that guy is power. That guy is about bringing it through your face. So, it's a one-two punch, totally two different styles and we have to be ready to adapt quickly."

Campbell said this is an Atlanta offense that will run it 30-plus times a game and won't get discouraged by any lack of success early on. They'll keep coming after a defense with it. He said if his defense gets a population of defenders to the football and closes gaps they'll be fine.

RELIABLE ROOKIE

Rookie tight end Sam LaPorta has been terrific as both a pass catcher and blocker through Detroit's first two contests. He's caught 10 passes for 102 yards. He's the first tight end in league history to record at least five receptions in each of his first two NFL games.

The rookie also hasn't been afraid to stick his nose into the run game. He's been responsible for making some pretty critical blocks to help spring touchdown runs. That's something tight ends coach Steve Heiden, who was a block-first tight end in his NFL playing days, appreciates about LaPorta.

"First of all, he went to Iowa, so he better know how to block," Heiden said with a smile Wednesday. "But the biggest thing is the kid is willing to stick his face in there and play big boy ball. You don't always find that in these young kids. He's willing to do it."

ROSTER MOVES

With the Lions dealing with a multitude of injuries the team has made a number of roster moves to start the week. They placed defensive back C.J. Gardner-Johnson and edge rusher James Houston on injured reserve.

The team signed running back Zonovan Knight and offensive lineman Kayode Awosika to the active roster from the practice squad.

They've also released defensive lineman Chris Smith from the practice squad and signed linebacker Mitchell Agude, cornerback Darius Phillips, running back Devine Ozigbo and offensive lineman Dan Skipper to the practice squad.