Barca's public pursuit of Griezmann has angered Atletico, who reported them to Federation Internationale de Football Association in December for making an illegal approach for the player and followed up with a statement in May telling Barca "enough is enough".
Messi is excited by the prospect of uniting with the 27-year-old and believes he would go a long way to helping Barca become European champions for the first time since 2015. This (the World Cup ) starts on Saturday, so it will be defined this week. "I think we will find out this week".
Atletico were hit by a transfer ban and in a show of loyalty, Griezmann pledged himself for another year to the Madrid outfit.
The Atletico Madrid ace has always been linked with a big-money move to Camp Nou and has resolved to clarify his club future this week.
"I can only say that to win the Champions League you have to have the best players". The deal, should he sign, will make him the club's highest paid player; and the entire club has been endorsing the deal since it was offered - from the president right down to the kit man.
Asked if Griezmann is the top summer target Barca need, Messi told Spanish newspaper Sport: "I don't know if he's a priority". It depends on the technical secretary and coach.