The 27-year-old is now a rumoured target for LaLiga champions Barca, who are said to be keen to activate the reported €100 million release clause in his contract, which runs until 2022.
Having seen the club continue to develop after the exits of star strikers Sergio Aguero, Radamel Falcao and Diego Costa, Forlan is confident Atleti could cope with Griezmann leaving.
"There was [Sergio] Aguero, [Radamel] Falcao, Diego Costa and others came in. No player is above the club. Life goes on," Forlan told El Transistor.
"The same thing happened with Griezmann when Atletico signed him from Real Sociedad. If we complain that Barca buy him it would be hypocritical.
"Everyone takes advantage of their moment and if the player wants to go, they go."
Forlan believes the pressure is on to claim a second Europa League crown under Diego Simeone.
"If Atletico are the favourite because of what they have won, they have an obligation to win the Europa League," he added.