Some days I think I would definitely like to move abroad but then, other days, I think I don't fancy it at all," he told Kicker when asked about United's interest. "Basically ... I think moving abroad would be good for my professional and personal well-being. Eventually, I'd like to leave the Bundesliga.
"I have had many conversations with the leaders of Dortmund, where I know I am a big part of the team, but I am yet to make a decision about my future.
"I'm being open about this because I'm not a fan of those who claim they are staying but, behind the scenes, have actually secretly agreed a transfer away from their current club.
"I will do what is best for my career and what I would like to do. Everyone knows how much I love it at Dortmund but I also want to make sure I'm part of a strong team with powerful players.
"Whether we are in the Champions League, the Europa League or have no European football at all, it will play no part in my decision-making.