Manchester United are wasting little time in the transfer market following their Premier League heartbreak and are interested in Borussia Dortmund striker Robert Lewandowski, according to the player's agent.

Having lost out of Manchester City in the title race, United are set to spend big in the coming transfer window, and Sir Alex Ferguson has already identified one of his summer targets.

Both he and assistant boss Mike Phelan were present during Saturday evening's German Cup final which saw Dortmund prevail over Champions League finalists Bayern Munich.

The double winners are likely to be inundated with interest in their star turns, with Shinji Kagawa, Mats Hummels and Mario Gotze having all impressed during the club's back-to-back title wins.

Dortmund have begun by offering new deals to the likes of Lewandowski to warn off interest from afar, however the Pole has rejected the possibility of an extension, with his future at the Bundesliga side now uncertain.

Robert Lewandowski
Lewandowski scored 22 goals in the league this season.

"I can confirm that the (new contract) offer of Borussia Dortmund is insufficient," his agent Maik Barthel told Bild.

"I am also able to confirm an interest of Manchester United in the services of Robert Lewandowski."

The 23-year-old finished as Dortmund's top scorer this season with 22 goals to his name, only behind Bayern's Mario Gomez and Schalke 04's Klass-Jan Huntelaar in the race for the golden boot.

The success of Papiss Cisse, who netted 22 goals in his penultimate season with Freiburg in the Bundesliga, since joining Newcastle United will give United a good indication of how seamless the step up to the Premier League can be.

Injuries to Danny Welbeck and Javier Hernandez led to a lack of continuity in United's attack this season, while the expected departures of Dimitar Berbatov and Michael Owen could leave their forward line wafer thin heading into the new season.

Sir Alex Ferguson has revealed that reserve team striker Will Keane will make the step up to the first-team next season after making his first appearance for the club in the Premier League defeat to Blackburn Rovers.

United and other admirers will have the opportunity to assess Lewandowski further during this summer's European Championships when he turns out for Poland, whom he's scored 13 goals in 40 games for.