Atletico Madrid striker Forlan leads Uruguay's semi-final challenge tonight against a Holland team tipped by Fergie to win the tournament.
Ferguson said: "I sent him a text the other day. He's been fantastic and we're all proud of him.
"There was never a problem with him at Old Trafford, it was just the combination of him and Van Nistelrooy did not work.
"The boy had other issues, his sister's health in Spain. He always wanted to get to Spain at some point. The only criticism of ourselves was that we sold him too cheaply.
"He could have been a hero. He was a great lad, a magnificent professional, spoke five languages and was a great tennis player."