Borussia Dortmund say Ilkay Gundogan's knee injury has left a question mark over a potential transfer, with the Germany midfielder heavily linked to Manchester City.

The 25-year-old is set to miss the rest of the season, including this June's European championships in France, after dislocating his knee cap in training with Dortmund.

His current Borussia contract expires in June 2017, but he has been linked to a transfer to Manchester to work with their incoming manager Pep Guardiola, after Gundogan's agent met City's director of sport Txiki Begiristain in Amsterdam in March.

But Gundogan's latest injury has now cast doubts over a possible switch.

"Ilkay is currently still in shock (after getting injured). How things go with him, we will have to wait and see," Dortmund's director of sport Michael Zorc told German daily Bild.

Gundogan has been capped 16 times by Germany, but already missed his country's triumph at the 2014 World Cup because of a long-term back injury.

According to Bild, a year's extension to his Dortmund contract is out of the question, meaning Gundogan may have to sign a long-term deal with Borussia if a possible transfer falls through.

"An injury would be the worst reason to extend a contract," admitted Dortmund's coach Thomas Tuchel.

Gundogan has put in a series of strong performances this season for Dortmund this, who will finish second behind Bayern Munich in the German league and face Guardiola's Bavarians in the German Cup final on May 21 in Berlin.