The German World Cup winner has been heavily linked with a move away from Bayern this summer, with recent media reports claiming that Louis van Gaal is considering a bid to bring the forward to Old Trafford.
Reports this week have claimed that United are considering a €100m bid for the player.
And Lahm admits that he is not sure where Muller will be playing his football next season.
Lahm told Sport1: “That is not my decision.
“In football everything happens so quickly, therefore, you can never issue a guarantee.
“And that is why I cannot give guarantees on behalf of Thomas Muller.”
United have already snapped up Bastian Schweinsteiger from Bayern Munich this summer as Van Gaal looks to transform his side into genuine Premier League title contenders next season.
The Red Devils, who finished fourth in the Dutchman’s first campaign in charge at the club, kick off their new top-flight season with a home clash against Tottenham Hotspur on the opening weekend.
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