Howard makes the claim in his upcoming autobiography, suggesting that Friedel tried to ensure Howard would fail to obtain a work permit for his move to United from Metrostars.
In his book, Howard claims:
I needed character references from other players. Manchester United asked former U.S. captain John Harkes, the first American to play in the Premier League, and they asked Kasey Keller and Brad Friedel, among others. Most signed without question.
However, Man U told us that Friedel had refused to submit a statement on my behalf.
"You're kidding me," I said. Friedel was among what was then a handful of American players in the Premier League; his influence was huge. Having himself been denied several times, he understood better than anyone exactly what was at stake. Why wouldn't he vouch for me?
I mean, who would sabotage his own countryman like that?
The legal team at Manchester United ... told me that Brad hadn't merely refused to sign a statement on my behalf, he had actively tried to block my transfer. He'd written to the appeals committee suggesting that I shouldn't be given a work permit at all."
They are extraordinary claims and seemingly at odds with an American soccer culture that tends to stick together when it comes to promoting its sportsman beyond their shores.
"There is no letter. I never sabotaged, and I never stood in the way of Tim Howard getting a work permit. This is ludicrous.
"It's complete garbage. To be honest with you, all we're looking for is an apology. We can't get the book reprinted. I'm not looking for monetary gain. I just want an apology."
Friedel then goes on onto reveal he did not refuse to sign a character reference, but instead refused to sign a letter of support given to him by then US coach Bruce Arena to aid Howard's work permit appeal.
"I said, 'Sure.' It was sent to me, and the only thing that was true on it was my name. The letter was full of exaggerations that the people on the PFA [Professional Footballers' Association] and appeals committee would have seen through.
"It said that I had been in direct competition with Tim Howard for the starting job on the U.S. national team for the last two years, when anyone who follows [U.S.] soccer knew it was between Kasey [Keller] and I.
"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."
When asked about what he would do now, Friedel confirmed he was not keen to drag it through the courts.
"I don't want to litigate against a fellow professional, against a fellow American and a goalkeeper.
"I've seen Tim quite a few times over the last 10 years. Never once has he ever turned his shoulder or not said hello or anything, so to all of a sudden put this crap in a book, that's showing a lot of bravery. I don't get it."
It is certainly a bizarre spat that appears to centre around specifics and speculation. And I would have thought both men would have got round the table by now to thrash out their differences and establish what exactly went on.
I think Friedel hit the nail on the head though when he was asked why he thought Howard had decided to makes these accusations now if they were apparently inaccurate:
"Perhaps he was getting pressure from the publisher to put something controversial in the book."