In his new autobiography 'Faf: Through Fire ', Du Plessis revisited the ill-tempered 2018 Test series between South Africa and Australia, which saw Warner, Steve Smith and Cameron Bancroft all hit with huge bans for their roles in a ball-tampering plot that was discovered during the third Test.
In his book, Du Plessis accused Australia of ball-tampering during the first Test as well, with Warner at the centre of his allegation. "During the first Test in Durban, the Australian pace attack had got the ball to reverse insanely," he wrote.
"Mitchell Starc claimed nine wickets and, although I regard him as one of the best proponents of reverse-swing bowling I have ever seen or faced, those deliveries in Durban were borderline unplayable. He would come in around the wicket with a badly deteriorated ball and get it to hoop past us.
"Our balls had also reversed but not nearly as much as theirs. We suspected that someone had been nurturing the ball too much to get it to reverse so wildly, and we watched the second Test at St George’s through binoculars, so that we could follow the ball more closely while Australia was fielding.
"When we noticed that the ball was going to David Warner quite often – our changing room must have looked like a birdwatching hide as we peered intently through our binoculars. There was a visible difference between how Mitchell Starc got the ball to reverse in the first Test in Durban and the final Test in Johannesburg.
"We now know that there was an obvious reason for that." And in an interview with BBC Sport about his book, Du Plessis said Australia "abused" his side throughout the first Test of that series and described Warner in particular as a "bully".
"Australia wanted to bully us," Du Plessis said. "We had to stand up for ourselves. They abused us that whole game but the way we fought back turned the series around.
"He [Warner] was a bully. I don't have time for bullies."