Nick Kyrgios has hit back at Bernard Tomic via Twitter after his fellow Australian accused him of faking illness in order to miss a Davis Cup tie against the United States.
Tomic went down in four sets to John Isner on Sunday, ensuring Australia were defeated on home soil in their World Group first-round tie.
During a change of ends in his loss to Isner, Tomic could be heard criticising Kyrgios' withdrawal from the team - telling captain Lleyton Hewitt: "Nick's sitting down in Canberra. Bulls*** he's sick. Two times he's done it. Two times he's faked it."
Tomic then sparked further controversy in a news conference by saying he would lose respect for Kyrgios should the latter return to action at Indian Wells next week.
The comments provoked an angry response from Kyrgios, who tweeted: "Heat of the moment, not gonna take it personally. Indian Wells a week away, plenty of time.
"Just don't expect me to have your back anytime soon."
In addition, Kyrgios mocked Tomic's 28-minute defeat to Jarkko Nieminen at the 2014 Miami Masters, writing in a post that was subsequently deleted: "Let's not forget who holds the quickest loss on the ATP tour lol #howmanyminutesagain"
The row will cause a headache for recently appointed Australia captain Hewitt, who faces a challenge to restore unity in an apparently fractured team.