Manchester United manager Alex Ferguson said he sold striker Ruud van Nistelrooy to Real Madrid because the Dutchman could not deal with being dropped.
Ferguson told a news conference in Amsterdam on Thursday that most players accept losing their place in the team but Van Nistelrooy, who has moved to Real for 11 million pounds, was different.
"It's how they react and adapt to being left out that counts," said Ferguson. "Ruud was different in that way and so that's what happened."
Van Nistelrooy, 30, who scored 150 goals for United in 219 games, was dropped for February's League Cup final win over Wigan Athletic in favour of France striker Louis Saha and later struggled to guarantee a first-team place.
He has described the breakdown in his relationship with Ferguson as "very painful."
Ferguson added: "The difficulty with footballers today is the satisfaction you have to give them in terms of picking the team.
"So every time you pick a team there are two or three players you're hesitant about telling they are not playing.
"Maybe they are big players or have been a big player for you in the past. Or maybe you have a special relationship with them.
"You hope they will agree with reasons for leaving them out but sometimes a player doesn't and I can understand that."
Ferguson was promoting the Amsterdam Tournament which begins on Friday when United play Porto.
He took the opportunity to meet Ajax's defender Jaap Stam with whom he famously fell out before selling him five years ago to Lazio and the pair exchanged a friendly chat and a handshake.
"He was a great player for me, won the European cup with me, what can I say?" said Ferguson.
"Business is business, sometimes you get an offer you can't refuse and that's the way we felt about it, nothing else."
He also confirmed United's interest in Villarreal's Spain midfielder Marcos Senna, but added: "There is interest in other players as well."
