EXCLUSIVE | By Spain correspondent Miguel de Souza

Iker Casillas is expected to tell Real Madrid that he will leave this summer, throwing fresh doubt on the future of David de Gea at Manchester United.

Football Insider sources understand that Real have targeted De Gea to be Casillas’ long-term successor at the Bernabeu and have been given encouragement by the United goalkeeper’s failure to extend his current contract, which expires in 14 months.

De Gea is negotiating a new deal with United, and the Premier League giants remain hopeful he will agree new terms, but the strong possibility remains that he will eventually end up at Real.

The Spanish giants are likely to be in the market for a new ‘keeper in the summer if, as expected, Casillas brings to an end his 16-year reign as the No1.

The 33–year-old Spain record-appearance holder has a contract that runs until 2017 but he has spoken of his interest in experiencing a new club after spending his entire career at the Bernabeu. Football Insider sources have learned that Casillas is increasingly likely to tell senior officials that this will be his last season at Real.

The Champions League holders signed Keylor Navas last summer and the Costa Rican has deputised for Casillas on seven occasions this season, including against Levante last month.

Navas is well regarded at the Bernabeu but De Gea is viewed as the long-term successor to Casillas.

The keeper, 24, has had an outstanding season for United and is in the running for the individual player-of-the year awards alongside the likes of Eden Hazard and Harry Kane.