Nickel back Buster Skrine remains in concussion protocol and will miss his first game of the season Sunday when the Bears host the Houston Texans at Soldier Field.

Skrine sat out practice all week after sustaining a concussion in last Sunday's loss to the Detroit Lions. The 10-year NFL veteran has recorded 66 tackles, three pass breakups and one forced fumble while appearing in 12 games with one start this season.

Top candidates to replace Skrine Sunday against the Texans include veterans Sherrick McManis and DeAndre Houston-Carson and second-year pro Duke Shelley.

"Those guys, they've done a great job at being able to fill in at these specific positions when guys are down, then when we get into different packages, they've shown it all year long," said coach Matt Nagy. "What they do is they rely on their savviness at that position and understanding schematically what other teams do.

"So when you have a time like this where you've got Buster who's out, you've got to have other guys step up. Whether it's Duke Shelley or whether it's Sherrick or whether it's DHC, it's a great opportunity for them. I just love the way they practice. I love how serious they take the game. So when a guy goes down like that or is out, it's a great opportunity for them, and they've all had a really good week."

Selected by the Bears in the sixth round of the 2019 draft out of Kansas State, Shelley has appeared in 16 games, all as a reserve, in his first two seasons with the team, playing only eight snaps on defense last year and just six so far in 2020.

"I would say his arrow is up," Nagy said, "and I'd say it because of this: It took him a little bit of time to learn the speed [of the NFL] and learn the new defense, but now he's getting a little bit, naturally, more confidence in himself. And then he gets to learn from one of the best nickels in the game [in Skrine]. That's a really good thing to have, and he's accepted that. He's really accepted it. Is he going to still make mistakes? For sure. But one thing that he does is he's a ballhawk. He's usually around the ball and he's got good ball skills."

Outside linebacker Khalil Mack (shoulder) returned to practice on a limited basis Friday after sitting out Wednesday and Thursday and is listed as questionable. Mack has been limited in practice due to back, knee and shoulder injuries throughout the season—and listed as questionable—but has yet to miss a game.

In other Bears injury news, outside linebacker James Vaughters (knee) has been ruled out of Sunday's game, while tight end J.P. Holtz (shoulder/knee) is questionable after being limited in practice all week.

Receiver Darnell Mooney did not practice all week because of an undisclosed personal issue. But Nagy indicated Friday that the rookie receiver likely will be active Sunday, saying: "I do feel good about where he's at and having him play."

For the Texans, tight end Pharaoh Brown (concussion) is out, while quarterback A.J. McCarron (non-injury); receivers Brandin Cooks (foot/neck) and Keke Coutee (knee); linebacker Jonathan Greenard (illness); and cornerbacks Keion Crossen (foot), Phillip Gaines (knee/shoulder) and John Reid (neck) are all questionable.