Borussia Dortmund are facing up to the possibility of losing two key players this summer after the agent of Robert Lewandowski claimed a deal is being worked on for the Poland international to leave the Westfalenstadion.

Lewandowski scored all four goals as Dortmund thrashed Real Madrid 4-1 in the first leg of their Champions League semi-final on Wednesday night but much of the post-match talk centred around his future. His contract expires at the end of next season, leaving Dortmund in the unenviable position of having to decide whether to cash in this summer or risk seeing the 24-year-old leave on a free in 2014.

Reports in Germany on Thursday suggested they have opted for the former with the player's agent, Maik Barthel, suggesting Dortmund have sanctioned his departure. "We have reached an agreement with a club and intend [him] to move this summer," Barthel told Sport Bild.

"There is a very interesting offer for Robert which fulfils entirely the demands set by Dortmund and also the demands of Robert. Dortmund have assured us that Robert can move at the end of the season under these conditions. We stick to agreements and now it's up to the clubs to sort things out."

Barthel stopped short of naming the club in question but speculation suggests it is Bayern Munich, who earlier this week agreed to activate the €37m release clause of the Dortmund playmaker Mario Götze. Losing two of their best players to their closest domestic rivals would be a major setback for Dortmund, who are also likely to meet Bayern in the Champions League final after the Bavarians' 4-0 defeat of Barcelona on Tuesday night.

"We are getting 37 million for Götze which we don't even want," said the coach, Jürgen Klopp, echoing the words of the club's general manager, Hans-Joachim Watzke, who said he could "do without" a transfer fee for Lewandowski, as long as he stays for another year.

Watzke added on Sky television: "Our wish is explicit that he stays here. It all surprises me. We are willing to do without a transfer fee for him [if he leaves as a free agent in 2014]. I have had plenty of wishes in my life which have come true."

Götze and Lewandowski combined for Dortmund's opening goal against Madrid on Wednesday night before the former Lech Poznan striker took centre stage, netting three more times to leave José Mourinho's side with an uphill task at the Bernabéu next week.

His performance was no surprise given his record this season. He has scored 34 goals in 42 games and has netted in each of his past 12 Bundesliga appearances.