Manchester United boss Sir Alex Ferguson has been warned he must cough up big for Borussia Dortmund striker Robert Lewandowski. Lewandowski, 24, has been on Fergie's radar for the last 12 months.

United held talks with the German outfit in the summer but failed to agree a fee for the hitman, whose current contract expires in June 2014.

A Dortmund source told the Daily Star: "If United want him, they will have to spend big because he is so valuable to Dortmund. He is one of the best strikers in Europe now and won't come cheap."