Davis Cup captain Hewitt told reporters at Melbourne Park late on Thursday that he had banned Tomic from playing in the Australian team after receiving physical and verbal threats, including "blackmail", from the 26-year-old.
World number 88 Tomic returned serve on Friday, describing Hewitt as a "liar".
"I have never threatened his family," Tomic told News Corp Australia.
"Nice, Lleyton. To think how low of a person you actually (are) and (it's) why the Australian public never liked you.
"I got nothing to do with your family and I don't care what's wrong with you, you liar."
Tomic triggered the war of words after being dumped from the Australian Open first round.
At his post-match media conference, he called for twice Grand Slam champion Hewitt to be replaced as Davis Cup captain and accused him of favouritism in the awarding of wildcards to the Australian men's players in the draw.
(Reporting by Ian Ransom in Melbourne; Editing by Amlan Chakraborty)
