Casillas remains the number one choice for the Spanish national team despite spending the early part of the campaign on the sidelines for Real Madrid.
However, Valdes's form this season has led to claims that the Barcelona keeper should be handed the position.
"We know that we have three great goalkeepers in the team. Whoever plays, does so well. The other day, Iker made a brilliant save, kept things at 0-0, with one of his magic feet," Fabregas told reporters at a press conference.
"And Victor we have seen with Barcelona make saves like against David Villa at the Camp Nou, and Arda Turan. And the saves he made in Valencia, Malaga... he is one of those goalies that gives you titles, Leagues, games and many points for the end of the season.
"This is why they are the best, the most wanted and why there is this discussion today around who should be in the team."
Spain face Chile in a friendly on Tuesday.