Allegedly Barca boss Tito Vilanova wants back-up to keep first choice custodian Victor Valdes on his toes.
The former ADO Den Haag youth team player was an ever present last term and, having let Fraser Forster move to Celtic, Krul is a player Alan Pardew would be loathed to lose.
Krul has played a major part in the Dutch national team set-up, challenging Roma’s Maarten Stekelenburg for the starting spot in Louis van Gaal’s line-up.
Victor Valdes has barely been challenged as Barcelona’s number one for eight seasons and back-up option Jose Pinto is not thought to be the best stand-in.