Manchester United and Arsenal are watching Napoli defender Kalidou Koulibaly.

Il Mattino says Koulibaly's form this season has attracted interest from both English heavyweights, along with Barcelona.

The defender is tied to Napoli until 2019 and Napoli are eager to upgrade his deal to 2021, with his salary doubled to €1.6 million.

Napoli now rate Koulibaly in the €20 million class.

Just this week, Napoli legend Diego Maradona declared the defender good enough for Real Madrid or Barca.