The two teams meet this week in the Champions League.
"Sir Alex explained my position as soon as I arrived. I knew I was going there to be an understudy to Fabien Barthez, and I learnt a great deal from him - playing with my feet, for a start. It was about being prepared to fight for the No1 spot.
"Clearly, there were games I would rather forget about, not least the one at Spurs, but United gave me four years of unbelievable achievement. When I look back at 70, I'll be able to say that I played for the best team on the planet," he told the Sunday Telegraph.
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