Manchester United boss Sir Alex Ferguson admits it is difficult to make the final decision on his retirement - as he wants to go out at the very top. The 65-year-old shelved plans to step down in 2002 and showed his desire for trophies was as strong as ever last season when United won the title after a four-year hiatus. And he hinted that he is loathe to step down until the likes of Wayne Rooney and Cristiano Ronaldo take the current team to their optimum level. 'The thing is I have not made my mind up when I'm retiring,' Ferguson said. 'It's not going to be an easy decision. 'The important thing is to leave a good team. The present team is very, very good but they will get better.' Ferguson believes his assistant Carlos Queiroz will be a strong contender to replace him but does not know how American owner Malcolm Glazer will approach the most difficult task of his reign. 'Thankfully I don't have to make the decision,' said Ferguson, who is approaching his 21st anniversary as Old Trafford boss. 'I have a great assistant in Carlos Queiroz, I think he will be a strong candidate.' But he added: 'We have new owners now and I don't know how they look at the situation over in America. 'They have been great supporters of everything we have done but they may have their own ideas.' While Queiroz was the only name Ferguson mentioned when asked who he would choose as his successor, the Scot also revealed a number of up-and-coming managers who have impressed him in recent years. The Glaswegian told an audience at the Citizens Theatre in his home city that he admired Alan Pardew, Sunderland boss Roy Keane and Newcastle manager Sam Allardyce. 'Pardew at Charlton has got something about him, he is a good young manager,' Ferguson said. 'Roy Keane has got a good chance, he has something about him. 'Of the older ones, Sam Allardyce is a very influential manager. 'His way of managing is very different. He is very into the sports science, he had about 16 people working behind the scenes at Bolton. 'He knew how many yards his players were running, how many sprints they were making. 'During the game he has got all the figures on a big screen behind the dug-out. He will do well at Newcastle.'