Casillas is reportedly expected to leave Real Madrid this summer [Reuters]

Iker Casillas' future at Real Madrid is once again scrutiny, amid the whistles of his own fans and reports claiming the Spanish giants are likely to replace him with Manchester United star David de Gea at the end of the campaign.

The Spanish legend fell out of favour with a big section of the Santiago Bernabeu fans when former manager Jose Mourinho opted to bench him in favour of Diego Lopez in the 2012-2013 season.

Casillas looked to repair the damage little by little under Carlo Ancelotti last season. Even though he remained Real's second-choice in La Liga, he was the number one in their march to both the Champions League and the Copa del Rey crowns.

Ancelotti decided to close the debate in the summer by parting ways with Lopez, who joined Milan, while signing the little-known Keylor Navas to stand in for Casillas in minor games.

However, the debate has reopened in recent times after some made Casillas the scapegoat for Real Madrid's humiliating 4-0 defeat to Atletico earlier this month.

Last week a poll by Madrid-based newspaper AS – the majority of whose readers are Real Madrid fans – revealed more than 75% of respondents preferred Navas to Casillas in the starting line-up for the weekend game against Deportivo.

Ancelotti overlooked the fans' opinion by keeping Casillas in his XI, but many fans expressed their disapproval during the game by whistling him every time he touched the ball.

The 33-year-old recently revealed he considered leaving Real Madrid last summer due to the uncertainty surrounding his position, but eventually opted to stay one further season in his boyhood side.

When asked about the fans' reaction, he said: "Everyone has a right to think what they like.

"When the public whistles it is because they are right to. I can merely go out and play and do my best."

However reports in Spain claim that the keeper is actually growing frustrated about the boos and has renewed his plans to leave the team in the summer.

Should the reports prove true, it would be a massive blow for United in their attempts to convince De Gea to stay at Old Trafford.

Los Blancos have reportedly earmarked the United star as the main target to replace Casillas. While it looked as though they may wait until the summer 2016 - when De Gea's contract at Old Trafford expires - the Casillas departure would probably accelerate the process.