Howard has claimed in his soon-to-be published book The Keeper that fellow American Friedel attempted to "sabotage" his move to Manchester United from the New York MetroStars by refusing to endorse the younger goalkeeper's work permit application.
But in an interview on Wednesday, Friedel demanded an apology, arguing Howard's claims were "complete garbage".
Friedel claimed he had been contacted by Howard's representatives to sign a letter supporting the then 24-year-old's application but was forced to make some changes because it was "full of exaggerations".
"It said that I had been in direct competition with Tim Howard for the starting job on the US national team for the last two years, when anyone who follows soccer knew it was between Kasey [Keller] and I," Friedel told ESPN FC.
"Yes, I refused to sign that. We got the letter and said 'We have to change this, because this isn't true'.
"We made our changes and sent it back. They didn't like what I was going to sign so they didn't use it. And that was the end of the matter."
Howard's book includes allegations that Friedel contacted the PFA, telling them not to give Howard a work permit but PFA CEO Gordon Taylor rejected that claim on Thursday.
"With regard to the appeal by Manchester United on behalf of Tim Howard, which was successful, we have been asked to confirm that the PFA did not receive any correspondence from Brad Friedel in opposition of Tim Howard's work permit application," he said in a statement released on the PFA's website.
Howard went on to make 45 Premier League appearances with United over three seasons before joining Everton, where he remains, having played 311 games in England's top tier for the Merseyside club.
Friedel, 43, remains on the books at Tottenham, although he is their number two goalkeeper behind Hugo Lloris, with the veteran having played over 400 Premier League matches during stints at White Hart Lane, as well as with Aston Villa, Blackburn Rovers and Liverpool.
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