Benfica are facing a battle to keep Serbian midfielder Nemanja Matic in January.

The Portuguese club claim they have had strong interest from agents working for Manchester United and Borussia Dortmund.

They want around £20million for the former Chelsea reserve, who went to Benfica as part of the David Luiz deal.

Champions United are keen to strengthen their midfield in January.

After missing out on Cesc Fabregas last summer, they have subsequently lost Michael Carrick to injury, while Marouane Fellaini needs a wrist operation.