The Catalan giants are reportedly awaiting a decision from the France international as to whether he wants to join, having also been offered an improved contract by Atleti.
Barca already have Luis Suarez, Ousmane Dembele and Messi in their forward line, but the latter believes that additional firepower could be required if his side are to end their recent dry spell on the continental stage.
"I am in agreement that to win the Champions League again we need to have the best players - Griezmann is one of them," he told Sport. "If the club sign him, brilliant. I don't know if he's the priority. That depends on the signing committee and the coach.
"I can only say that to win the Champions League you have to have the best players. And he is very good."
Barcelona have failed to progress beyond the quarter-final stage in three seasons since last lifting the Champions League, being knocked out by Atletico, Juventus and most recently Roma.