Carlo Ancelotti's side were less than three minutes from defeat in the final against Atletico Madrid, after Casillas conceded from a set-piece - as Diego Godin looped a header over the Spanish custodian, who was drawn off his line.
Casillas, Real's captain, was not made to pay for the mistake, though, as Sergio Ramos equalised for Real, before goals to Gareth Bale, Marcelo and Cristiano Ronaldo in extra-time capped a 4-1 win.
Speaking to Marca, Raul said despite his error, Casillas was still a worthy winner of the European cup.
"Iker has had a great Champions League and a great season," said Raul, who won three Champions League titles with Real during his 16-year spell in Madrid
"He was unlucky with the goal, but if Madrid got to this final it is because he had many good days.
"He doesn't have to prove anything.
"I'm very happy for everyone and especially him that he was able to lift the European cup."
Such was Casillas' elation at sealing the European title, he claimed the UEFA trophy was more important to him than any success with Spain at the World Cup.
