An independent Football Association regulatory commission suspended Kiko Casilla for eight games after being satisfied the Leeds goalkeeper called Charlton’s loanee striker Jonathan Leko “a fucking nigger” during a game at the Valley in September last year.

Casilla maintains his innocence and has been supported by Leeds, who have questioned the FA’s decision to decide the case on the balance of probabilities, but, in a 62-page document explaining the “written reasons” for its decision, the FA insists the required burden of proof was exceeded.

The FA had wanted to impose a 10-match ban on Casilla but the independent panel comprising Graeme McPherson QC, Marvin Robinson and Stuart Ripley decreed eight games would be a fairer sanction after reaching a unanimous decision that the Spaniard had racially abused Leko as he punched the ball clear following a corner.

Although they accepted the former Real Madrid goalkeeper has limited English they did not believe Casilla’s assertion he had never heard of the word “nigger” before Leko, who was on loan from West Brom and had clashed with the goalkeeper in the lead-up to the corner, made his accusation.

While Leko’s version of events was endorsed, convincingly in the panel’s view, by Charlton’s Macauley Bonne, another witness – Arsenal’s former Leeds loanee Eddie Nketiah – recalled hearing the goalkeeper and striker exchange insults at the set piece but did not hear the particular word in question. “I just remember hearing swear words throughout the corner being taken,” Nketiah said.

On Tuesday night Charlton condemned the abuse Leko and Bonne have been subjected to on social media and hailed their bravery in confronting racism. “The club is pleased there is finally a resolution,” they said in a statement. “However the club is disappointed with the abuse on social media they have received. Jonathan was a victim and the pair of them did not ask for this. The club is proud of them for standing up as football continues to fight racism.”

The FA defended its use of the civil standard “ balance of probabilities” as the burden of proof in these cases, rejecting the Leeds argument the criminal standard of “beyond reasonable doubt” would be more appropriate.

After pointing out that balance of probabilities is widely used by professional bodies, including the General Medical Council, it said that in Casilla’s case “In reality we were satisfied to a degree well above the requisite standard,” the FA said.