The intimidating Dutch central defender spent three years with the Red Devils after arriving from PSV Eindhoven, making 79 league appearances and helping United lift the treble in 1999.
However, Stam's relationship with both Ferguson and the club ended in controversial circumstances following revelations in his autobiography that the Scot had approached him without PSV's permission.
Stam was sold to Lazio for £16.5 million and later played for AC Milan and Ajax before retiring in 2007.
Ferguson said in the Independent in September 2007 that: "It was an offer I couldn't refuse. But in playing terms it was a mistake."
And he has since revealed that he still considers the defender's sale one of his biggest errors throughout his hugely successful career of more than 23 years at the club.
"It was one of the mistakes I made, hopefully I haven't made too many, but that was one," he said in the Mirror.
"I got this offer from Lazio for £18.5 million. Was it £18.5 million? No, £16.5 million I think it was, and I said 'Can't turn it down. He's 30 years of age.'
"I thought if we could get Laurent Blanc for a year or so and bring the young ones through like Wes Brown and John O'Shea, but it backfired.
"Jaap and I have got on well together. We spoke the last time we were over in Holland at the Ajax tournament. I spoke to him for a long time there and everything’s fine."
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