Bolton manager Sam Allardyce has confirmed defender Abdoulaye Faye suffered a mild concussion during The Trotters' 1-0 win over Blackburn on Sunday.
The Senegalese stopper clashed with Jussi Jaaskelainen in the first half at Ewood Park and was eventually replaced by Quinton Fortune.
Faye was taken to hospital after struggling to overcome the knock to his head following his substitution at half time.
The 28-year-old has now been ruled out of the midweek Carling Cup tie against Charlton and is also a major doubt for the visit of Manchester United at the weekend.
"Abdoulaye was visibly in pain and was taken to hospital as a precautionary measure on Sunday," Allardyce told the club's official website.
"He will have further tests this week from our medical team.
"He has been ruled out of Wednesday's match at Charlton.
"If tests prove that he has fully recovered, he could return on Saturday against Manchester United."