Offensive lineman Marcus Martin, who started the 49ers’ first 14 games, sat out another day of practice Thursday due to a concussion he sustained on Sunday.
Martin must pass all phases of the NFL’s concussion protocol to be available for Sunday’s game against the Detroit Lions. Martin must return to non-contact football activity and be cleared after undergoing contact simulation.
With Martin’s availability in question, the 49ers would likely start Sunday how they finished last week’s game against the Cincinnati Bengals – with Daniel Kilgore at center, Eric Pears at right guard and rookie Trent Brown at right tackle.
Martin was injured early in the fourth quarter against the Bengals when his head struck linebacker Rey Maualuga’s leg during an attempted downfield cut block on a failed screen pass.
Running back Shaun Draughn (knee), guard Alex Boone (knee) and linebacker Michael Wilhoite (ankle) have not practiced this week.
Five 49ers starters saw limited practice time on Thursday due to injuries: receiver Torrey Smith (back/foot), defensive lineman Quinton Dial (shoulder), linebacker Ahmad Brooks (shoulder/back), cornerback Tramaine Brock (hamstring) and safety Jaquiski Tartt (knee).
Here are the participation reports from both teams from their Thursday practices:
49ERS
Did not participate
G Alex Boone (knee)
RB Shaun Draughn (knee)
C Marcus Martin (concussion)
LB Michael Wilhoite (ankle)
Limited participation
CB Tramaine Brock (hamstring)
LB Ahmad Brooks (shoulder, back)
DT Quinton Dial (shoulder)
WR Torrey Smith (back, foot)
S Jaquiski Tartt (knee)
Full participation
DT Arik Armstead (shoulder)
LB Navorro Bowman (shoulder, finger)
LB Eli Harold (shoulder, hamstring)
CB Dontae Johnson (ankle)
LB Aaron Lynch (concussion)
T Erik Pears (knee)
T Joe Staley (knee)
LIONS
Did not participate
CB Dwight Bentley (illness)
S Glover Quin (concussion)
Limited participation
LB Josh Bynes (foot)
WR Calvin Johnson (ankle)
DT Haloti Ngata (neck)
T Michael Ola (knee)
DT Caraun Reid (ankle)
G Larry Warford (quadricep)
