Damon Johnston, Herald Sun editor, echoed the cartoonist's in the paper's official statement on Tuesday.
Knight's caricature showed a butch and fat-lipped Williams jumping up and down on her broken racquet, having spat out a dummy.
Her opponent, Japanese and Haitian player Naomi Osaka, was shown as a blonde woman.
The caricature was published alongside unflattering cartoons of US President Donald Trump and North Korean Leader Kim Jong-un.
Knight now appears to have deactivated his Twitter account and has not commented since the outrage.
Cartoonist Paul Zanetti, a friend of Knight, said cartooning was under threat from political correctness, and the Herald Sun front page "spelt out exactly where we are at this point". "The world has just gone insane", Knight said in a reply to the criticism published in Tuesday's Sun.
An Australian cartoonist has come under withering criticism for portraying tennis superstar Serena Williams using - what Harry Potter author JK Rowling described as - "racist and sexist tropes".
"In her straight sets loss to Naomi Osaka, Williams was simply outplayed and lost her temper in a huge and ill-disciplined blow-up".
It's entirely possible to be critical of Serena Williams' outburst and hold her accountable for her behavior without debasing her and crossing a line that many find offensive. The tournament referee's office docked Williams $10,000 for "verbal abuse" of chair umpire Carlos Ramos, $4,000 for being warned for coaching and $3,000 for breaking her racket. Some black women say Serena Williams' experience at the U.S. Open final resonates with them.
An Australian illustrator has justified his portrayal of Serena Williams at the US Open after the went viral and he was accused of being a sexist racist.
However, it was quickly slammed by critics around the world who compared the image to a Jim Crow-era representation of black women.
'Ramos is tough, one of the best umpires in the world, he did what he had to do in that match, because she overstepped the limit.
Knight's cartoon was criticised after some audiences perceived racist undertones in the exaggerated features present in his depiction of Williams.
"To argue the Williams drawing is racist is an attempt to defeat cartooning - and satire - with a politically-correct barrage". Williams protested that and demanded an apology from the umpire, who penalised her a game.