Leyton Orient boss Russell Slade is worried about Lee Butcher after he was injured during the 3-1 home defeat to Scunthorpe.
The stopper's knee appeared to buckle beneath him as he attempted to collect a cross in the closing minutes of the game, allowing the Iron to score their third goal.
"It's not looking too good for him," said Slade. "He's with the medical team but I can't tell you exactly what he's done but the symptoms aren't too good.
"Their third goal was entirely due to his injury - he's gone up in the air to collect the ball and gone down on one knee which unfortunately has gone from underneath him."
Slade lamented his side's second-half performance in his 100th match in charge of the club.
"There were two contrasting halves. We got an element of control when we scored the opening goal and I thought we deserved our half-time lead but, after that, we just didn't go out and play," he said. "We didn't do the simple things well, we didn't control the ball well, I didn't think we passed the ball well, we didn't attack people in midfield. It was difficult for me to find a positive spin on the second period and I'm really, really disappointed."