United boss Sir Alex Ferguson and his assistant Mike Phelan watched Borussia Dortmund’s cup final win over Bayern Munich in Germany on Saturday.
United have long been linked with a move for Dortmund midfielder Shinji Kagawa, but the club is also reportedly interested in defender Mats Hummels and Polish striker Lewandowski.
“I can confirm that the (new contract) offer of Borussia Dortmund is insufficient,” Maik Barthel told Bild.
“I am also able to confirm an interest of Manchester United in the services of Robert Lewandowski.”
Lewandowski has scored 22 goals for Borussia Dortmund this season.
