The Germany international has long been regarded as one of the Premier League's club top targets and previously indicated that he would be open to leaving Dortmund last month.
Speculation over his future continues to persist, but when pressed on the topic by Bild, Hummels said: "I don't want to talk about that topic constantly.
"I did it a few weeks ago - and that must be enough."
Asked about reports of a bid from United, Dortmund sporting director Michael Zorc replied: "I can't confirm this."
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