It's impossible to say when I'll retire, insists United's French-speaking boss Sir Alex Ferguson

Ferguson indicated in an interview with French radio that he would bow out in three years.

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However he played down the situation in his media briefing before the FA Cup match against Portsmouth tomorrow at Old Trafford.

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Turning the air blue: United boss Sir Alex Ferguson

He said: "It is something I have said quite a bit. If your health is good and you are enjoying your job, it could be two or three years.

"I am not going to pigeon-hole myself on that one.

"It could be four years, it could be tomorrow. It is impossible to put a time limit on something like this."

Britain's most decorated boss will have spent 25 years at the helm at Old Trafford, should he retire in 2011.

Ferguson has won 18 trophies after arriving at the club in November 1986 from Aberdeen - and remains anxious for more.

United are still in line for the treble for the first time since 1999 and are odds-on to defeat Portsmouth.

They are also aiming to retain their league title and have already booked a place in the quarter-finals of the Champions League this week after beating Lyon.

Ferguson had initially planned to retire in 2005, only to change his mind.

That decision was vindicated as he rebuilt his side, going on to claim last season's Barclays Premier League crown.

Radio interview: Sir Alex Ferguson

"I'm getting beyond the future now, " Ferguson told a French radio station.

"I still have a lot of passion. I'm still happy. But I'm 66 now - maybe three years more, then I'll finish."

Ferguson said it was too soon to mark out his successor.

But he added: "I have a great assistant in Carlos Queiroz. He will come into the reckoning.

"But we have owners and a chief executive who will choose the new man in three years' time."

Ferguson can speak some French as well as a bit of Portuguese and has been putting his new language skills into practice.

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"I enjoy speaking to Patrice Evra, Louis Saha and Mikael Silvestre because it helps improve my French, " he told Red View.

"Portuguese is also quite prominent here and I am picking up a few words along the way.

"Carlos (Queiroz) can speak Spanish, Italian, Portuguese, French and English..it's very handy.

"The joke around here is that in the dressing room the second language is English."