The Daily Star says United boss Sir Alex Ferguson has not forgotten the 31-year-old, who claimed his fourth goal of the World Cup in the 3-2 semi-final defeat by Holland on Tuesday.
Atletico Madrid star Forlan said: "Sir Alex sent me a text, wishing me luck, and I always had respect for him and him for me.
"There were great players at United, I didn't have the chance to play, it was fair.
"I was trying to look for a place, it was difficult and I moved to Villarreal."
And the Uruguay star did not rule out a United return.
"They will have to decide," he said when asked if he was interested.