Sheffield Wednesday look set to be without Jordan Thorniley when they host Swansea City this weekend.
The uncompromising defender suffered concussion in Saturday's hard-fought 2-2 draw at relegation-haunted Rotherham United.
Thorniley received lengthy treatment on the pitch from the Owls' medical staff after an aerial collision with Millers midfielder Will Vaulks and was eventually replaced by debutant Dominic Iorfa, who grabbed an equaliser in the 10th minute of added on time.
The Football Associations's concussion protocols state a six-day recovery period. The Owls entertain 13th-placed Swansea on Saturday.
Steve Bruce, the Owls boss, told The Star: "Jordan is struggling for the weekend because of a bit of concussion. I would think the Swansea game will be too early for Jordan."
It is the second time in the space of a year Thorniley has sustained concussion. He was also stretchered off at Millwall in the 2017/18 season after colliding with the leg of Lions midfielder Jed Wallace in the build up to Steve Morison's winning goal. Thorniley was taken to hospital after suffering bruising to his face and concussion.
"We have to monitor Jordan," said Bruce. "He had a bad head injury last year.
"We are going to play it by ear and let nature take its course."
Captain Tom Lees is in pole position to step in for Thorniley. The 28-year-old has resumed full training, having missed the last three fixtures due to a shin problem.
Bruce said: "Tom is training again. Everybody is okay.
"We have got Dominic (Iorfa) who can also play at centre-half if I need him to play there. Dominic gives us a little bit of flexibility as well."
Josh Onomah, on loan from Tottenham Hotspurs until the end of the campaign, remains on the sidelines because of a hamstring injury. The midfielder strained his hamstring in Bruce's first match in charge of the Owls against Ipswich Town earlier this month.
"He is still receiving treatment at Tottenham," said Bruce. "It was a pretty nasty one and a shame for him.
"I would think it is at least a couple of weeks before we see him back here."