Manchester United manager Alex Ferguson has revealed that Nemanja Vidic is making slow progress in his recovery from a calf injury, and could be out for longer than first thought.

The Serbian defender was withdrawn during United's opening-day win at West Bromwich Albion, and although initial estimates put him out for six weeks, the Scot has said that he is no closer to a return.

"It's slow progress with Nemanja," said Ferguson.

"Calves can be troublesome. He's not done any training [and] he's not making any great progress at the moment."

Premier League leaders United will try to maintain their 100% start to the season at Stoke City on Saturday.