Krul began his career at hometown club RAS and later local Eredivisie club ADO Den Haag. He joined Premier League club Newcastle United in the summer of 2005 on a three-year deal after failing to sign professional terms. ADO demanded a compensation fee and objected to the FIFA Dispute Resolution Chamber (DRC). The DRC denied the claim and ADO took the case to the Court of Arbitration for Sport (CAS). CAS ruled in February 2007 in favour of ADO, ordering Newcastle to pay €220,000 as compensation for the transfer.