#1 Jaap Stam
Selling Jaap Stam to Lazio for £16.50 million in 2001 was Sir Alex's worst mistake and the greatest club manager of all time acknowledges it. He said the move made sense financially, but in the footballing sense, it was Sir Alex's most imprudent decision.
Jaap Stam is of the best centre-backs to have played in the Premier League.
He was known for possessing a rare combination of speed, strength and ball-playing ability as well as an excellent positional sense. With him at the back, United rarely conceded goals. He played at United at a time when the team had a great mix of players (Ryan Giggs, Paul Scholes, Roy Keane, Dwight Yorke, Andy Cole, Nicky Butt etc.) who could mix finesse with solidity.
Stam was signed from PSV Eindhoven for £10.6 million. The lofty fee made the most expensive Dutch footballer at the time. Spanning three seasons, he made 127 appearances for the club scoring just once. Guess all he knew was to not let anyone score goals! He won the treble of the Premier League, the FA Cup and the UEFA Champions League in his first season with the club. He also won the Premier League in both of his remaining seasons with the club and also claimed the 1999 Intercontinental Cup.
After leaving United at the end of the 2000-01 season, he played for Lazio, AC Milan (where he helped the club reach the 2005 Champions League final) and Ajax before retiring in 2007. At present, he is the manager of the Eredivisie side, Feyenoord.