Manchester City striker Sergio Aguero could have joined arch-rivals United when he was just 17, according to football agent Barry McIntosh.
McIntosh, speaking exclusively to the Daily Mirror, revealed Manchester United sent their former chief scout out to to watch the Argentine international.
Aguero has since gone on to play for Atletico Madrid and Manchester City - becoming one of the world's most potent strikers.
Aguero joins a long list of stars who former Red Devils boss Sir Alex Ferguson missed out on - joining the likes of Ronaldinho, Arjen Robben and Gareth Bale.
"I remember when I was in Argentina scouting and I recommended Aguero to Sir Alex's brother Martin Ferguson to take him to Manchester United," said McIntosh.
"Martin went and saw him play for Independiente against Huracan and Aguero was available for Euros 3.5million as a 17-year-old.
"Aguero has gone on to play for Atletico Madrid and is now at Man City which is ironic."
Aguero's late goal against Queens Park Rangers at the end of the 2011/12 season makes United's transfer blow even harder to take - as his goal allowed City to win their first Premier League title.
"Radamel Falcao, I saw him playing wide right for River Plate back in 2008.
"I identified if this boy was given a chance upfront he would do well," added McIntosh.
"In the end he is the one that put Andre Villas Boas on the map and won the Portuguese league with Porto and the Europa League."