Mats Hummels' future remains a mystery

After Borussia Dortmund sealed a return to the capital to compete for the German Cup, captain Mats Hummels revealed how much the decision over his future is affecting him.

"It's a very difficult decision," Hummels told Sky television after Dortmund's 3-0 win against Hertha on Wednesday. "When I decide, then everyone will understand why it has been so difficult for me. For the last few weeks, it's almost certainly cost me half an hour before bed every night, because it's so personal," said the 27-year-old.

With a World Cup, three Bundesliga titles and a German Cup to his name, the decision to make a change could just as well be a personal one as a professional one. The lure of the Champions League - the one thing missing from Hummels' cabinet - will likely play a role, though, and is the reason Barcelona are one of the names rumored to be interested.

Bayern an option

Hummels, like his club, suffered a dip in form last season and felt the critics were singling him out. This season, with his fitness concerns seemingly behind him, he has returned to the form that saw him become such an instrumental member of Germany's World Cup winning squad in 2014.

Speaking to "SportBild," Hummels' father and agent, Hermann Hummels said: "Mats is on the verge of a huge decision in his career, in his life. Dortmund are back in Europe's elite again, and that's why the decision is so tricky for him. If he does leave, then he can only go to one of the top five, six clubs and of course Bayern Munich are one of those."

Dortmund chairman Hans-Joachim Watzke told the Munich-based daily "Süddeutsche Zeitung" that he would "fight for Mats like no other player" ahead of what looks to be a summer of change for the club. Midfielder Ilkay Gündogan, whose contract also ends in 2017, has been heavily linked with a move to join a Manchester City team that will be coached by Pep Guardiola.