BERLIN (AFP) - Borussia Dortmund say they are "fighting" to keep Germany midfielder Ilkay Gundogan, amid reports he has already told Barcelona he will join Pep Guardiola at Manchester City next season.
Second-placed Dortmund play Bayer Leverkusen, who are third in the Bundesliga table, on Sunday hoping to close the gap behind runaway league leaders Bayern Munich.
Dortmund have won 15 of their 21 games so far in Germany's top flight and defensive midfielder Gundogan, who has a contract until 2017, is in superb form.
But according to Spanish newspaper Sport, Gundogan has broken off negotiations with Barcelona and told the Catalan giants he expects to join City next season to play under Guardiola, who leaves Bayern at the end of the season.
Sport say the 25-year-old Gundogan has already told Dortmund that he will not be extending his contract.
"Really? We should know about that, shouldn't we? Truth is, we don't know anything about that," replied Borussia Dortmund's official account on Twitter to Sport's claims.
Dortmund coach Thomas Tuchel says they are working hard to keep Gundogan, who is back to his best after missing most of the 2013/14 season with a back injury.
"We are fighting to keep him and I believe it's not the case that there isn't a chance he'll stay," said Tuchel.
"The importance of Ilkay in this form is undisputed, but one can imagine that the interest from other clubs is very high." Dortmund's chief executive officer Hans-Joachim Watzke says he expects to be able to announce a decision on Gundogan soon.
Meanwhile, French newspaper L'Equipe claims Pierre-Emerick Aubameyang, who is under contract at Dortmund until 2020, is destined to play for Real Madrid - due to a promise he made to his grandfather.
"Auba" has scored 30 goals this season, 20 of which have come in the Bundesliga, and is rivalling Bayern's Robert Lewandowski as the league's top scorer.
"In 2014, just before the death of my grandfather, who was born in Avila 100 kilometres from Madrid, I gave him the promise to play one day for Real," Aubameyang told L'Equipe.
"It'll be complicated, but this (promise) is anchored to a corner of my heart."