Derek Carr to sit out Friday’s preseason game with rib injury, Nate Burleson mulling retirement in 2015 and more

There wasn't much on the injury front Thursday, but some big-name players did manage to return to practice. Oakland Raiders quarterback Derek Carr was not one of those players. The Raiders play the Green Bay Packers in preseason action on Friday, and Carr will have to miss the game due to a rib injury, according to NFL.com.

Carr has been cleared from his concussion, but he's still dealing with bruised ribs. Not only would that be particularly painful, there's a lot of potential for further injury if he's playing on Friday. This likely means that Matt Schaub will wind up being the starting quarterback when the regular season gets underway, as some thought Carr could parlay a strong performance in this game into a starting opportunity.

But for the good news: Miami Dolphins running back Knowshon Moreno is now expected to make his preseason debut on Saturday against the Dallas Cowboys, according to Armando Salguero of the Miami Herald.

Moreno was a free agent addition this offseason after a strong year with the Denver Broncos. But he's not guaranteed a starting job and is battling with Lamar Miller. Moreno's injuries have limited him throughout camp and he hasn't played a snap in the preseason, so Saturday will be his big opportunity to show the Dolphins what he can bring to the table.

Then there's rookie Jadeveon Clowney for the Houston Texans. Clowney left Wednesday's practice with an injury and was being examined in the medical tent. He did not return, and was held out of practice on Thursday. It's unclear what the nature of his injury is at this point, but the Texans are saying it's not serious.

Lastly, Arizona Cardinals safety Tyrann Mathieu was cleared for 11-on-11 drills and was doing them on Thursday, according to Kent Somers of azcentral.com. Mathieu was recently taken off the physically unable to perform list, and while he's not taking hits just yet, his swift return to practice is definitely a good sign. He probably won't play in the upcoming preseason game, but being ready for the season opener is getting more likely by the day.

The San Francisco 49ers are trying to set the nickel cornerback position, and it's looking more and more like rookie first-round pick Jimmie Ward is the guy. Ward has been starting in the nickel throughout most of training camp and the preseason, but most figured that was due to Perrish Cox starting in place of Tramaine Brock, who is injured.

But on Wednesday, Ward remained starting in the nickel spot when Brock returned to practice. It sounds like that's how it's going to look when the 49ers take on the San Diego Chargers on Sunday, as well. Cox is a dependable veteran, but the 49ers might just consider him a backup at this point, with Ward maintaining a role in the nickel.

The Tampa Bay Buccaneers right guard spot is still up for grabs, and another player got thrown into the mix on Thursday. The Buccaneers traded safety Kelcie McCray for offensive lineman Rishaw Johnson from the Kansas City Chiefs, according to Tom Pelissero of USA Today.

Johnson doesn't have a ton of experience, but he did start one game and played in three with the Chiefs last season. This is his third year in the league and he's in the mix for the starting job. He joins a group that includes Oniel Cousins, Jamon Meredith, Kadeem Edwards and Patrick Omameh. It still appears to be anybody's job at this point.

Cleveland Browns wide receiver Nate Burleson is contemplating retirement at the end of this season, according to Nate Ulrich of the Akron Beacon Journal. Burleson is 33 years old and is entering his 12th season in the NFL. He's been productive in recent years, but has struggled with injuries.

He played in just six games in 2012 and was off to the best start of his career in 2013 before he broke his arm and was out for the season after nine games. Now with the Browns, Burleson is expected to get significant playing time if Josh Gordon is to serve a suspension (of any length). Burleson did say he's hoping for a big year to go out on if he does retire in 2014, for what it's worth.

Dallas Cowboys defensive end Anthony Spencer is hoping to avoid a stint on the physically unable to perform list, as reported by Todd Archer of ESPN Dallas. Spencer is dealing with a knee injury after coming back from microfracture surgery. He played in just one game last season, and is working toward his return. He won't be ready for the season opener on Sept. 7 and is a longshot for the team's Week 2 matchup.