The Sun says Atletico believe they will lose the French striker in the summer and are already planning for his exit.
An Atletico Madrid source said: “We know now we are going to lose Antoine, it is a matter of when not if.
“The club are hoping they can keep him and Diego Simeone for one last season, going into the new ground.
“It is going to be tough, though, as some big clubs around Europe are looking at buying him for a lot of money.”
United could face competition from Paris St-Germain and Bayern Munich.