After his uncomfortable showing in Spain's shock 5-1 loss to the Netherlands on Friday night, many are wondering whether it's time for the Spanish captain to make way for young blood.
Only recently turned 33-years-old, the Real Madrid and Spanish legend has shown glimpses in recent seasons that he is perhaps not at the level he has so often displayed over the many years he has been his club and country's number one.
Dropped by Jose Mourinho last season for Diego Lopez, Casillas has continued to be overlooked under Carlo Ancelotti in the campaign just gone. These two coaches, two of the best in world football, clearly saw something that persuaded them to drop somebody that was before then untouchable.
Casillas did walk away with the Champions League trophy this year, but not after playing his own unwanted part in Atletico's opening goal, which for a long time looked like it would decide the contest.
Once again in Brazil, the Spanish captain proved that he is at best a little rusty after a season of limited playing time, and at worst, into decline.
In reserve, Spain have one of the top young goalkeepers in the world, and a man surely likely to be their number one when the next World Cup kicks off in Russia.
After a troubled start at United following his move from Atletico, David de Gea has proved himself arguably the best goalkeeper in the Premier League, and was one of the few plus points of what was a disappointing season at Old Trafford.
Now with 133 appearances for the Manchester outfit, the 23-year-old matured significantly this season, and more than deserves a chance to come in and prove his worth to the ailing World Champions.
In all likelihood, it would be a surprise if De Gea get's the nod even if Casillas was dropped. He only made the squad after Victor Valdes was ruled out with injury, and Pepe Reina has much more experience around the Spanish camp despite spending almost nine years as backup to the Real Madrid man.
Of course, even the very best player has difficult games, but it is Casillas' inability to reclaim his Real Madrid shirt on top of these shaky performances that seem to vindicate any doubts in the player.
As the future of Spain, it is hard not to consider the possibility of giving De Gea a chance, perhaps even before the tournament in Brazil is over.