Despite a disappointing four-year spell at Old Trafford under boss Alex Ferguson, hitman Forlan raved about the Scot when Atletico Madrid team-mate David De Gea asked for advice.
The Uruguay star told The Sun: "David is a very good keeper with a bright future. He asked my advice about moving to United and we talked about it a lot.
"It is a great place to experience as a player.
"The manager is a legend, the staff are all really good and the fans were always very supportive of me, even when I wasn't scoring."