Manchester United boss Sir Alex Ferguson has raised concerns about Nemanja Vidic's long-term fitness ahead of the Serbian's return from injury.

Vidic has only managed 13 appearances since the start of last season having suffered from injuries to his calf, cruciate ligament and knee.

The 31-year-old has been included in the United squad to face Sunderland tomorrow, but Ferguson likened his injury problems to those suffered by Gary Neville towards the end of his career.

"We hope we've given him the proper rehabilitation. He's not had a lot of football so it is an issue, but we're hoping he sails through. There will be opportunities for him because he brings that great experience, that warrior type of defending he's for," said Ferguson.

"I don't know whether I will start him tomorrow but at least we have him back and given the number of injuries we've had to defenders over the last two or three years, it's a bonus for us. Getting an injury is an issue for players going into their late 20s and early 30s because they start to wonder how many years they've got left.

"For instance, Gary Neville was 32 when he got his injury and he never really recovered from it. He had recurring injuries - it was his calf, then it was his groin, then it was his hamstring, his ankle, it was just a catalogue of injury after injury simply because at that age recovery is a bit more difficult."

United currently sit six points clear at the top of the Premier League table.