By FOX Sports Staff
Casillas has recently recovered from a hand injury and found himself on the bench after January signing Diego Lopez's good run of form.
Carlos, who played alongside Casillas during his playing days at Real Madrid, believes that Casillas must not give up on the fight for the starting berth under Jose Mourinho.
"Iker has always been a starter and I wasn't expecting him to be injured. Neither was I expecting Diego Lopez to return to the club and perform so well," Roberto Carlos told Marca.
"Mourinho is his own man, he has his own way of doing things and you have to respect that.
"Now Iker will have to fight for a spot because nowhere in his contract does it say that he will be in the starting XI for the next forty years."