Time is running out on the 49ers getting two of their top offensive playmakers ready to face the Cincinnati Bengals.
Running back Elijah Mitchell on Thursday sat out his second day of practice this week while he works through the NFL's concussion protocol.
Wide receiver Deebo Samuel, who sat out the 49ers' Week 13 game against the Seattle Seahawks with a groin injury, has not practiced this week, either.
Stay in the game with the latest updates on your beloved Bay Area and California sports teams! Sign up here for our All Access Daily newsletter.
The 49ers (6-6) return to action on Sunday against the Bengals (7-5) at Paul Brown Stadium.
Mitchell is the 49ers' leading rusher with 759 yards and five touchdowns on 165 carries for a 4.6-yard average.
Samuel is the team's leading receiver with 56 catches for 1,006 yards and five touchdowns. Samuel has added 203 yards and five touchdowns on 25 rushing attempts.
San Francisco 49ers
Find the latest San Francisco 49ers news, highlights, analysis and more with NBC Sports Bay Area and California.
Linebacker Fred Warner had his second full day of practice in a row after missing the first game of his NFL career on Sunday against the Seattle Seahawks with a hamstring injury.
Linebacker Dre Greenlaw did not practice due to a groin injury, which he sustained two weeks ago after missing nine games following surgery to repair a core muscle injury.
Cornerback Emmanuel Moseley is expected to miss multiple games with a high ankle sprain.
For the Bengals, quarterback Joe Burrow took part in limited practice after sitting out Wednesday's practice with an injury to the small finger on his throwing hand.
Linebacker Logan Wilson is expected to miss an extended period of time with a shoulder injury. Wilson, a second-year player, is having a breakout season with a team-leading 92 tackles and four interceptions.
Here are the full participation reports from the 49ers' and Bengals' practices on Thursday:
49ers practice report
Did not practice: RB Trenton Cannon (concussion), LB Dre Greenlaw (groin), DL Maurice Hurst (calf), RB Elijah Mitchell (concussion, knee), CB Emmanuel Moseley (ankle), WR Deebo Samuel (groin)
Limited: None
Full participation: DL Nick Bosa (not injury related - resting player), LB Marcell Harris (concussion), C Alex Mack (not injury related - resting player), LB Fred Warner (hamstring), T Trent Williams (not injury related - resting player), RB Jeffery Wilson (knee)
RELATED: Shanahan's lack of trust in Jimmy G crystal clear to Young
Bengals practice report
Did not practice: CB Chidobe Awuzie (foot), RB Chris Evans (ankle), RB Joe Mixon (illness), DT Tyler Shelvin (illness), LB Logan Wilson (shoulder)
Limited: QB Joe Burrow (right finger, knee), WR Tee Higgins (ankle), LB Markus Bailey (neck), C Trey Hopkins (ankle), T Riley Reiff (ankle)
Full participation: LB Joe Bachie (knee), DT D.J. Reader (not injury related - resting player)