Town could be without Matt Preston for a period of time with the defender set to see a specialist on Friday.
The defender, who has been in superb form in recent weeks, picked up the knock during the 1-0 win against Mansfield on Saturday.
The initial scan didn't return positive results and Preston will now seek a second opinion, although Town Boss Dave Flitcroft has already prepared himself for the worst case scenario.
"He's got to see the specialist on Friday," Flitcroft said.
"He's had a scan and, at the minute, it doesn't look good.
"There was a load of swelling on it on Sunday and he had the scan on Monday night.
"His knee has absolutely ballooned - it doubled in size.
"We are sending him to a top specialist on Friday and he'll give us the details.
"The adrenaline got him through the game on Saturday and he felt something after the game. It blew up after and it could be a medium-term injury.
"I can't clarify that until after he sees the specialist.
"It would be a massive loss.
"He had a great start when he came in, he then had an indifferent spell but, since then, his form has been fantastic throughout the last couple of months."