The Spaniard has also been slapped with a £60,000 fine and instructed to attend an educational course.
Leko, on loan from West Bromwich Albion, made an official complaint to the FA following Charlton’s 1-0 win against Leeds in September, where Casilla was accused of using foul word on the 20-year-old.
The former Real Madrid shot-stopper has consistently denied making any racist comment, but insists he respects the FA’s verdict.
"I feel truly sad and devastated for being accused of making supposedly a racist comment during last September's match vs Charlton," said Casilla in a message on his Twitter page.
"With respect to the FA, I fully respect and understand the obvious process to be taken to prosecute any accusation of racism.”
“In fact, I totally agree with any prosecution to eliminate any trace of racism in sport.”
"I do not feel at all that the guilty verdict is a clear reflection of the incident."
Leeds have issued a statement condemning the FA’s decision to ban their number one goalkeeper, who has featured in all 35 league matches for the Peacocks this season.
A club statement read: "The FA panel have based their decision on the balance of probability rather than proving Kiko to be guilty beyond reasonable doubt, which we have always believed is the more appropriate burden of proof."
