As David Warner fired another barb at Cricket Australia (CA) with an incendiary social-media post, Cummins' version of events has been rejected by Chadd Sayers.
Sayers, a member of the Australian Test touring party in South Africa in 2018, said every player knew sandpaper was being used on the ball.
His comments contradict Cummins' denial, and support Usman Khawaja's recollections.
"I believe that everyone in that side knew what was going on and what was being used," Sayers told SEN radio on Sunday.
Sayers said Australia also used sandpaper on the ball in the second Test, preceding the now-infamous third match of the series in Cape Town, where the tourists were busted by television cameras.
"In Port Elizabeth ... it was used in two Test matches," Sayers said.
"And there was discussions in changerooms of how we were going to get the ball to reverse and what was going to be used.
"I just know that there was numerous conversations of it around in the changerooms."
Sayers, who didn't play in the Port Elizabeth or Cape Town Tests, sad he took the sandpaper from the field after it was used on the ball in Port Elizabeth.
"I just knew that it was going to be used, as I believe everyone else did," said the retired South Australian quick, who played his only Test in the fourth and final match of the series.
"The plan was that Cameron Bancroft was going to take that out, the ball was going to be dropped on the ground by the umpires, and he was going to go about business.
"It (the sandpaper) was given to me to take off, so that wasn't planned or anything, I was just the player who took the drinks out at the time."
Sayers backed Khawaja's statement that the entire touring party discussed taking collective responsibility, after Bancroft was caught by television cameras with sandpaper in his trousers during the Cape Town match.
"After the occurrence in Cape Town, we all sat in the change rooms after that day's play and probably for 60 to 90 minutes, we talked about what had happened and, I guess, where to next," he said.
"I guess at that stage we probably didn't know the severity back in Australia as well."
Sayers felt "awkward" when watching Cummins denying knowledge of the sandpaper plans when the Test skipper dismissed Khawaja's version as nonsense at a media conference on Friday.
"I didn't like how he did go at Usman and got personal," Sayers said.
"I probably get why. But I just don't think it needed to happen."
Meanwhile, Warner says he wasn't given all the evidence before taking the brunt of the punishment for Sandpapergate.
On Saturday, Warner posted on Instagram that: "As far as I am aware, CA did not interview Josh Hazlewood, Mitchell Starc or Nathan Lyon in their 2018 investigation.
"If that's correct then how can CA push the idea that the bowlers didn't know?
"It looks like they had decided who they wanted to blame from the very beginning ... ran a shoddy investigation to serve the purpose and now they want to maintain the false narrative that the bowlers had no idea.
"That stinks of a cover up."
After numerous media reports confirmed bowlers had indeed been interviewed by CA in its investigation, Warner on Sunday again took to Instagram to support his previous post.
"Just to clarify 'As far as I am aware' was the POINT," he wrote.
"I was never told the bowlers had been interviewed or provided statements.
"That information would've been pretty useful when I was forced to make decisions back in 2018.
"Why weren't we given all the evidence by CA?"
The internationally retired batsman was suspended by CA from all cricket for 12 months and stripped of the Test vice-captaincy.
Steve Smith was also suspended for a year by CA and lost the captaincy, while Cameron Bancroft was banned for nine months.
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