Griezmann wrote in his autobiography that he would be open to a move to United.
Atletico Madrid striker Antoine Griezmann has attracted criticism from his followers after posting an image on Twitter of himself dressed as a Harlem Globetrotter, sporting "blackface" make-up. If he did all he could for me as Griezmann does, I'll say it's no problem.
His contribution to Atletico's cause has improved in recent outings, but it would appear that the conjecture over his future during the close season has impacted the forward more than many thought it would.
"I don't like the January market just to buy [for the sake of it] but if you can buy a player in January that you would buy in June or July and can get him a few months before, then great".
Griezmann has struggled to find his best form for Atletico this season - at one stage going eight games without a goal - but has scored four times in his last five matches.
But he added: "I don't speak about players, especially players who belong to other clubs". "I am not ungrateful", Simeone said in the interview with the French publication.
Simeone insists he would not stand in the way of any of his players if they want to leave to develop their careers.
"I can't believe we're out here in 2017 saying don't dress up in blackface".
"Of course he can leave at some point, like Diego Costa and Arda Turan did in their day", Simeone told L'Equipe.