He added: “Nobody can foresee the future.
“I love it at Dortmund, but I can’t say that I’ll stay for two more years, or five or 10.
“It’s possible that a club could reach an agreement with Dortmund in June and I’ll go.
“I want to be honest: When you are ambitious and also want to see something else… it’s difficult to talk about.
“Some players have ambitions, and therefore they leave and want to experience something new, you know.”