epa03826554 A photo made available on 16 August 2013 shows singers and guitarists Kyle Gass (L) and Jack Black (R) from the US comedian rock band 'Tenacious D' performing on the 'Space Stage' during the Frequency Festival 2013 in St. Poelten, Austria, 15 August 2013 evening. The festival runs from 15 to 17 August. EPA/HERBERT P. OCZERET 
A video widely shared on social media from the concert in Sydney on Sunday showed Gass being presented with a birthday cake and Black urging him to make a wish. Gass then seemed to say "don't miss Trump next time" before blowing out the candles.
Trump was shot in the ear during a campaign rally in Pennsylvania on Saturday, which the FBI is probing as an assassination attempt. The former president has since attended the Republican National Convention with a thick bandage over his right ear.
Gass on Tuesday apologised on Instagram for his "severe lack of judgment" and said the comments were inappropriate, dangerous and a terrible mistake. Black said he was "blindsided" by the comments and that he would never condone hate speech or encourage political violence in any form.
"After much reflection, I no longer feel it is appropriate to continue the Tenacious D tour, and all future creative plans are on hold," Black said.
Black, who has starred in School of Rock, The Holiday and Jumanji and was the leading voice role in the Kung Fu Panda animated movies, has been a vocal supporter of Joe Biden and had attended a re-election fundraiser event for him in June.
Tenacious D was formed in 1994 by Gass and Black in Los Angeles where the duo performed their "mock rock" routines in local bars. Their show in Newcastle on Tuesday was cancelled and they were scheduled to perform in Brisbane, Melbourne and Adelaide, and in New Zealand later this month, before the tour was cancelled.
Gass's comments drew strong rebuke from Australian politicians including Australia's ambassador to the U.S. Kevin Rudd, who said people joking about violence made him feel sick and that they must "grow up and find a decent job."
Senator Ralph Babet of the United Australia party said the band should be deported immediately.
(Reporting by Renju Jose in Sydney; Editing by Michael Perry)