Anti-racism charity Kick It Out say they contacted Charlton to offer Jonathan Leko support after he was racially abused by Leeds' Kiko Casilla.
Leko said he had received "no contact in the way of support" from anti-discrimination bodies during the case.
An independent regulatory commission found Casilla guilty 22 weeks after the incident, with the goalkeeper banned for eight matches and fined £60,000.
Kick It Out say they "did reach out to Charlton within days of the incident".
Their statement continued: "We extend Jonathan Leko our sympathy as he did not receive the appropriate support he needed during this stressful experience."
Leko - who was on loan at Charlton from fellow Championship side West Bromwich Albion - also said he received "minimal contact" from the Professional Footballers' Association, who said they got in touch with Charlton and "did not hear back", apologising for "wrongly assuming" he did not need their support.
BBC Sport contacted Charlton for a response to the comments made by Kick It Out and the PFA, and the Championship club confirmed both parties were in touch with the club shortly after the incident.
"Our priority throughout that time was to support Jonathan Leko and McCauley Bonne through the process," said a Charlton spokesperson.
Leko's team-mate Bonne gave evidence to the independent commission hearing, having also reported to the referee that Casilla had made a racist remark while the match in September was in progress.
Kick It Out commended Addicks players for "bringing this to the fore" and also extended "an olive branch" to Leeds' Spanish goalkeeper Casilla, while also questioning the length of his eight-game suspension.
"This ban is in line with a similar case going back eight plus years and we would ask does it send a message that we have not moved on since that period of time," their statement added.
Charlton chairman 'saddened' by case
Charlton chairman Matt Southall says he worries football is "paying lip service" to tackling racism after Leko questioned the length of time for the case to be concluded.
"Reading his statement has left me deeply saddened," Southall said.
He wrote on Twitter: "Football has a duty of care to protect players who have been abused in this way. But if the process is too demeaning, lengthy or damaging, what does that say about how far we've truly come?"
Leko said he found the hearing "extremely stressful", making him doubt whether he would report similar abuse in future.
"To think a black player would consider not reporting racist abuse aimed at them is shocking," added Southall.
"To hear Jonathan so angry and distraught in his statement makes me wonder whether football as a sport is merely paying lip service to the fight against racism."
Charlton manager Lee Bowyer agreed the case "should have been dealt with quicker" but said the club "supported him [Leko] since day one".
"To have something like that hanging over you, especially as such a young player, has to be difficult to carry," Bowyer said.
"You could see he wasn't himself. He's a bubbly and confident lad and he was a bit quiet for a while after.
"But the group got him through that and he was himself again. While he was here, everyone was around to support him."
Leko's spell at Charlton ended prematurely in December, as a knee ligament injury ruled him out for the rest of the season and he returned to his parent club for treatment.
'You have to accept all the decisions'
The independent commission said it accepted that Casilla "is not a racist" and that the language "was wholly out of character", but that it was "satisfied on the balance of probabilities" that he had directed a racist remark towards Leko.
Casilla denied saying the racially-offensive word he was found guilty of using towards Leko, claiming that he was not aware of its "existence or meaning" until he was interviewed about the matter almost a month later.
Asked at a press conference on Thursday if Leeds "believe or stand by" that view, head coach Marcelo Bielsa said: "The people who have to judge Kiko have already done that.
"The people who represent Leeds, the club - what we do is accept the authorities' decisions.
"When a club is part of a competition, the clubs know that the authorities have the right to judge like they did in this situation, or another different situation when you accept the regulations when you are part of a competition, so you have to accept all of the decisions."
Responding to a question about Leko's statement, in which he spoke about a lack of support he had received while the process was ongoing, the Argentine added: "Any person who suffer racist abuse deserves the solidarity and support of everybody."
Bielsa was also asked about the "duty of care" towards Casilla, to which he replied: "We know that this is going to have an impact on his spirit and how he is.
"And of course any of us can be in a bad personal moment, for any reason, and we try to act in a human way.
"What we should avoid when we express ourselves, and for this reason I try to take care of the words I am using, because I don't want people to interpret that supporting Kiko at this moment means that we are in favour of racism.
"For this reason I say again - every person that suffers racist abuse deserves the support of all of us. But if any colleague of ours for any reason is suffering, we act in a human way."