The likes of Bayern Munich, Juventus, Manchester United and Manchester City are all believed to be keen on luring the Poland international away from Signal Iduna Park this summer.
BVB has so far stressed that the club has no intention of selling its star attacker, though a transfer now seems inevitable following comments made by the player's representative on the the back of one of the finest nights in the club's history.
"We have reached an agreement with another club and intend to switch clubs this summer," Barthel was quoted as saying by Sport Bild. "All of Borussia Dortmund's demands will be met."
Lewandowski's agent then went on to stress that BVB has promised the striker that he will be allowed to leave under the right conditions and expects Jurgen Klopp's side to honor its promise.
"There is an interesting offer for Robert that meets Dortmund's criteria and satisfies Robert's demands. BVB have assured us that Robert will be allowed to leave under these circumstances. It's now up to the clubs to sort it out."
The 24-year-old has a contract until the summer of 2014, with his exit another potential hammer blow for Dortmund following the news Mario Gotze will join rival Bayern Munich in the summer.