Borussia Dortmund manager Jurgen Klopp insisted Robert Lewandowski would not be leaving the club in the summer transfer window, despite widespread speculation over the Polish international striker's future.

Lewandowski has widely been tipped to leave the German club in the summer, after refusing to sign a new contract with the club; his current deal expires in 2014.

Manchester United and Bayern Munich, the club that Dortmund face in the Champions League final at Wembley Saturday, are thought to be the frontrunners for the 24-year-old's signature, with some reports suggesting a deal was already in place between Bayern and the striker.

However, Dortmund have always insisted they are doing their utmost to keep Lewandowski at the Westfalenstadion come next season, even saying they will be ready to lose him on a free at the end of next season rather that sell him this summer.

Klopp, who already faces the prospect of losing Mario Gotze to Bayern Munich next season, is convinced Lewandowski will stay with Dortmund next season.

"There is no topic of Lewandowski's transfer right now," Klopp told Polish newspaper Przeglad Sportowy.

"The rest of the team and I talk and think only about the final right now.

"My conclusion is that Robert is not leaving Borussia, and he will play here for the next season and I will be able to use him.

"That is why I don't want to even think about to which club he may fit better."

Lewandowski has been in terrific form this season, leading to some of the biggest clubs in the world chasing his signature. Apart from Manchester United and Bayern Munich, the likes of Chelsea, Manchester City, Arsenal and Real Madrid have also shown an interest.

It is unlikely that Dortmund will take the risk of losing one of their biggest assets on a free transfer; so unless they can agree on a new contract after the Champions League final, it does look like Lewandowski will be bound for a new club in the summer, which will be a pity for Klopp, who has created such an exciting and young team, capable of competing in the Bundesliga and Europe.