There was no rant, no histrionics, but a precise and deliberate character assassination. Despite his reputation as a player - quick to tackle, slow to forget - Roy Keane has more ice in his veins than fire, but those who cross him should not expect tolerance.

Yesterday his wrath fell on Jack Warner, the Fifa vice-president, or, in Keane's words, a “clown” and a “disgrace”. Warner, a special adviser to the Trinidad & Tobago Football Federation, wrote to Keane this week on Fifa-headed paper, protesting about the Sunderland manager's decision to withdraw Dwight Yorke from the World Cup qualifying match against the United States. The letter included phrases such as “callous disregard” and “a mean streak in your character”.

In Keane's defence, Yorke, who will turn 37 in November, has not played for Sunderland since suffering a fractured cheekbone in a pre-season friendly, yet he was permitted to report for duty with Trinidad this month and captained his country in the 1-1 draw with Guatemala on Saturday.

Yorke had announced his international retirement in 2007 but returned as a guest - at Warner's request - for the friendly against England in June. In that match Kenwyne Jones, the Sunderland striker, damaged knee ligaments and is out until next month. Yorke subsequently made himself available for the World Cup campaign.

The dispute has led Keane to regret awarding Yorke, his former Manchester United team-mate, a new one-season contract and, for the first time since his move to the dugout, to make withering criticism of one of his players. “I'm blaming Yorkie,” Keane said. “He's a clown as well. He's supposed to be retired. But he's on an ego trip. I wouldn't have given him a contract.”

Keane's dissatisfaction was largely reserved for Warner, a man the FA has been courting as it seeks to host the 2018 World Cup finals. “The man is a clown,” Keane said. “I spoke to him on Wednesday and told him what I thought of him and where I think he should go. He's writing these letters and it's under Fifa's heading just to impress everybody.

“Not once has he written me a letter about Kenwyne, who got injured playing in a friendly match for Trinidad. They even selected Carlos Edwards last season when he was out with a broken leg. I've always given support to players going on international duty, 100 per cent. It's just ridiculous that this clown is writing letters through the media.

“They don't insure their players, so we're footing a massive medical bill for Kenwyne. There has to be give and take. The word ‘clown' just suits him. I just told him he's a disgrace.”

Keane's broadside prompted another letter from Warner. “I chose to respond on a Fifa letter-head because your callousness showed utter disregard for Fifa's regulations,” he wrote. “May I remind you that a player's greatest honour is to represent his country, in spite of the fact that you chose to walk away from yours during the 2002 World Cup. Poor Sunderland.”