Ollie wrote in the Sunday Mirror: " The deal agreed between Palace and United for Wilfried Zaha is one where all three parties win.
"We receive a fee for a player who came through the ranks at Selhurst Park to win an England cap and we also get to keep him for the rest of the season to boost our promotion dream.
"United have bought a player who is as good as anyone I have ever worked with in my entire career as player or manager.
"And Wilfried will be joining arguably the biggest football club in the world and will be working under a manager who is a genius at improving footballers.
"But it has been a protracted process.
"At one point, I thought the deal would not be done - thanks to the input of a number of agents who tried to turn the player's head with ridiculous promises.
"One agent, in particular, acted absolutely disgracefully and although I won't give him the oxygen of publicity by naming him in my column, I will tell him exactly what I think of him the next time our paths cross.
"There isn't an agent in the world who can guarantee a footballer a move to Manchester United.
"Only the player himself can earn himself that kind of transfer - by playing so well that a manager like Sir Alex Ferguson feels compelled to sign him.
"So why on earth should an agent earn a vast amount of money when he has nothing to do with the player's development or either football club?
"The answer, in short, is that they shouldn't.
"It got to a stage when I was worried that Sir Alex would end his interest in Wilfried, such was the skullduggery of certain people who had nothing to do with Palace or United.
"So I decided to call the great man himself and assure him that Wilfried has all the physical and mental attributes to be a great success at Old Trafford.
"Whether my words to Sir Alex helped, I don't know.
"But earlier this season, I vowed to always do what I could to help one of my players to better himself. Even if that meant losing him."