MANCHESTER - Alex Ferguson, who should know the controversial Roy Keane better than most, would not venture an opinion on Friday about the ex-Sunderland manager's future. Keane, who played at Manchester United under Ferguson for 12 years, resigned from the Sunderland job on Thursday, leaving the club he steered to promotion in 2006 languishing in the Premier league relegation zone. "It's difficult to say whether he will be back or not. He was an incredibly controversial character," Ferguson said of the 37-year-old former United captain. "He always had something to say about the game. He was very controversial, of course, and as a player he was like that. He was a fantastic player and an interesting character," he told reporters. United face Sunderland at home on Saturday, a match billed earlier in the week as the master against the mentor. "Sunderland without Roy is a surprise," Ferguson said. "We just wish Roy well because he was a great player here and it's a pity." Ferguson said football was so volatile that it would not be the first time he faced a team without a manager. "Managers today are not lasting long so quite a few times I have experienced playing clubs that don't have a manager. "I don't know what to expect but what I do expect is my team to perform with the concentration and focus they had last Sunday. That was Manchester United back, I'm sure of it." United, who beat Manchester City 1-0 last weekend, are six points behind leaders Liverpool and five behind Chelsea with a match in hand.