Allen Park — Lions safety Glover Quin missed practice again Thursday due to a concussion, so it's looking increasingly unlikely that he'll be available for Sunday's game against the 49ers (1 p.m., FOX).
To return to play, Quin must pass the NFL's concussion protocol. Among the steps are returning to practice, which he'll have another chance to do Friday, and being cleared by an independent neurologist. After sitting Wednesday and Thursday, Quin will likely be questionable at best on Friday's injury report.
Quin has played 98 straight games and is the active ironman among NFL safeties, but a brain injury isn't like other injuries where he can simply deal with the pain.
"The doctors are in charge of that, and he hasn't been in our ear about anything," Lions defensive coordinator Teryl Austin said Thursday. "He knows that the doctors are going to handle it, and the neurologists, and they're going to make the determination on whether he plays or not."
In addition to Quin, cornerback Bill Bentley (illness) missed practice Thursday.
Wide receiver Calvin Johnson (ankle), defensive tackles Haloti Ngata (neck) and Caraun Reid (ankle), right tackle Michael Ola (knee), right guard Larry Warford (quad) and linebacker Josh Bynes were limited again.
Losing Quin would hurt, but the Lions have won the two games he left with injury, last Monday against the Saints and Thanksgiving against the Eagles. James Ihedigbo would play more if Quin sits while Isa Abdul-Quddus continues to start.
"We'll line up with 11, and we're going to play," Austin said.