Forlan represented Atletico between 2007 and 2011, scoring 74 league goals in 134 appearances.
However, the veteran forward believes that Simeone's improvement of the club since his own departure has been impressive.
"Simeone has contributed a lot," he told Goal.com.
"The team is in great form, fighting for championships with powerful teams that have a budget three times greater than that of Atleti.
"You can only admire what they are doing, the coaching staff and players."
Forlan is currently with his international squad at the World Cup.