Gordon Taylor has apologised after comparing the Hillsborough tragedy to the Ched Evans rape case.
"The last thing I intended to do was to upset anybody connected to the Hillsborough case," the Professional Footballers' Association chief said.
He added: "Ched Evans is a totally different case but he has the same belief of his innocence."
His apology has been accepted by some Hillsborough families but others feel it has compounded the issue.
Barry Devonside, who lost his son in the disaster, called Taylor "foolhardy".
"He really needs to connect brain with mouth," added Devonside.
Phil Scraton, a Hillsborough Independent Panel member and adviser to the bereaved families, had led earlier calls for an apology after labelling Taylor's comments "crass, insensitive and inappropriate".
And the author of the Hillsborough Families Support Group submission to the Home Secretary in 2009 - which called for a full review of the case - said Taylor's apology failed to address the issue as it still compared Evans' case to Hillsborough.
Scraton told the BBC: "He says they share the 'same belief'. Ched Evans has been found guilty in a court of law. He is a convicted rapist. No one was convicted of any crime at Hillsborough.
"Even after having this pointed out to him, Gordon Taylor still doesn't seem to understand the distinction."
Brenda Fox, who also lost a son during the Hillsborough tragedy in 1989, was more forgiving of Taylor.
"No hard feelings to the man at all," she told BBC Radio Merseyside.
"I think it was a mistake. It was just one of those off-the-cuff things that people say and they shouldn't say and they regret.
"Hopefully he'll be more careful and it will make him more cautious when he does speak."
She added: "I don't expect him to apologise to me personally. If he makes a statement that apologises to all the families, I will accept that and move on."
Ninety-six Liverpool supporters lost their lives at Hillsborough following a crush at the start of the FA Cup semi-final against Nottingham Forest at Sheffield Wednesday's stadium.
After years of campaigning for justice by the families of those who died, new inquests into the deaths began last year and continue in Warrington.
Scraton had earlier told BBC Radio 4 it was a "difficult time" for the families and survivors: "They are having to go to court every single day and sit through the longest inquests in British legal history."
Evans was jailed in April 2012 for raping a woman but continues to maintain his innocence following his release last year.
He was poised for a return to football with Oldham Athletic, only for the League One club to abandon the move on Thursday.
Reacting to that news, Taylor had drawn comparisons between the Hillsborough tragedy and the Evans case when he told BBC Radio 5 live that the footballer "would not be the first person or persons to have been found guilty and maintained their innocence and then been proved right".
Taylor added: "If we are talking about things in football, we know what happened, what was alleged to have happened at Hillsborough.
"It's now unravelling and we are finding it was very different to how it was portrayed at the time, indeed by the police at the time."
Ched Evans case latest developments
- Oldham drop their proposed move for Evans on Thursday following threats to the "club's staff and their families".
- Evans blames "mob rule" for the collapse of the Oldham deal.
- Prime Minister David Cameron says it was "unrealistic" of Evans to expect he could return to football straight away.
- PFA chief executive Gordon Taylor appears to compare Evans's case to the Hillsborough tragedy in a BBC interview.
- Taylor apologises for his comments, stressing he did not intend to cause any upset.
- The Football Association says it may change its code of conduct in light of the Evans case.
- Hull City manager Steve Bruce questions Evans's conviction and says he should be given a chance to play again.
During Friday's apology on BBC Radio Merseyside, Taylor said he had "long been a supporter" of the Hillsborough families.
He also insisted he had no plans to step down from the position he has held at the PFA for more than 30 years.
Evans, 26, looked poised for a move to League One club Oldham Athletic only for the deal to collapse on Thursday.
Sheffield United had also offered the Wales international use of their training facilities back in November, only to withdraw that offer following heavy criticism from patrons and sponsors.
Evans released a statement after talks with Oldham fell through, apologising for "the effects of his actions" but maintaining his innocence.
He blamed "mob rule" for the deal's collapse, claiming "the more radical elements of our society" had the "desired influence on some sponsors".
Read BBC Newsbeat's article on the definition of rape and consent.