The Serbian just recently signed a new contract with the German giants last summer but Subotic is reportedly open to offers.
Despite his wish to listen to suitors, the player's agent denies United have made any official approach for the defender.
"We are still waiting for offers," agent Stephen Kelly told Sport.
"He is calm and ready to represent his country. Talk about transfers does not bother him.
"Manchester United? We have held no talks, that is just a rumour without any substance.
"I am good friends with (Sir Alex) Ferguson but that wouldn't mean anything if talks do start.
"Will they? Maybe. Steven is a Dortmund player but there is a possibility he could leave the club this summer."
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