Underwater footage taken during the 100m breaststroke final shows gold medallist Cameron van der Burgh performing illegal moves at the start of the race.
In the race, in which Australian Christian Sprenger won silver, van der Burgh performs three dolphin kicks in quick succession before surfacing.
Under FINA rules each swimmer is only allowed one, and only after their hands have separated.
Swimming Australia has not commented on the illegal kicks and FINA refuses to use underwater technology to judge competitors.
The South African claimed the world record time of 58.46 seconds in Sunday's swim.
Former gold medallist and race commentator Grant Hackett said he was surprised by the footage.
"The breaststroke rule is only one butterfly kick and then you go into your underwater and then your breakout," Hackett said.
"By the looks of that start there were a couple of kicks in there, it looks pretty obvious.
"Then there was an additional kick once he glided out a bit further before he went into his technique."
Hackett said he thought FINA should consider using the underwater footage to make judgements about swimming technique in future.