Peterborough United midfielder Grant McCann will be out for up to 10 weeks after tearing his medial knee ligament.
The 31-year-old limped off in the second half of Saturday's 1-1 away draw with Leicester City.
The Posh captain has been influential for Darren Ferguson's side this season, scoring eight goals in 22 games.
"10 weeks is a worst-case scenario, but I hope I'm back as quickly as possible. I've always been a quick healer," McCann told BBC Radio Cambridgeshire.
"I've had operations on both knees before and I was back playing within four weeks. Fingers crossed, hopefully, I don't need an operation.
"It was a block tackle and my knee just opened up. I tried to carry on but it didn't happen," added the Northern Ireland international.
Ferguson has received better news on midfielder Lee Frecklington, whose knock against the Foxes should not rule him out of the this Saturday's home date with Coventry City.
And loan defender Scott Wootton is back at London Road after receiving treatment for a knee injury at parent club Manchester United.
Meanwhile, Ferguson says he wants goalkeeper Joe Lewis to stay at London Road, despite interest from Queens Park Rangers.
The 24-year-old has spent the past week on trial at Loftus Road.
"We're speaking to him about a new contract," Ferguson told BBC Radio Cambridgeshire. "We want to keep him, but we're still a fair bit apart.
"We need to do what's best for the club and, if we let him leave in the summer, then we'll get nothing for him."
Lewis, who submitted a transfer request back in January, has a contract with Peterborough which runs until June next year.
He suffered a serious knee injury during the League One play-offs in May, but returned to the Posh first team against Barnsley last week.
"It's my decision that Joe is currently in the side as Paul Jones cannot play every game," said Ferguson.
"Joe will either keep playing,as he did against Leicester, in which case we'll be fine, or QPR will take him in January and we'll get some money back."