FINA executive director Cornel Marculescu told Reuters the altercation that led to a complaint against Sun was the result of overcongestion in the warmup pool in Kazan and did not warrant further action.
“There was a misunderstanding in the pool,” Marculescu said.
“In Kazan, we have over 1,000 swimmers, so the preparation pool became very crowded.”
The Brazilian Aquatic Sports Federation said it made a formal complaint to FINA about Sun following a confrontation with a Brazilian female competitor during a warm-up session on the last day of the championships.
A Brazilian coach said Sun had tried to kick and elbow Larissa Oliveira after they collided with each other in the warmup pool.
Sun later withdrew from the final of the 1500 metres freestyle, an event he won at the previous world championships and at the London Olympics – and in which he holds the world record – citing a heart problem.
Sun apologised for pulling out of the race but neither he nor the Chinese Swimming Federation commented on the warmup pool incident.
He was later named as the best male swimmer in Kazan after winning the 400 metres and 800 metres.
“This is not, for me, anything special,” Marculescu said.
“(In the future) we need two preparation pools because one is not enough.”
Sun’s shock withdrawal from the 1500 metres caught most people by surprise, including FINA officials, who spoke to Sun before the race was due to start.
“We discussed it with the (Chinese) delegation and the federation and finally with him and he said it was some health problem,” Marculescu said.
“His coach was also debating with him, a little bit stronger, to make him swim but he said he can’t.
“He’s a great star, he’s a great swimmer. But with the young people, you never know.”
Sun became the first Chinese man to win an Olympic swimming gold medal when he took the 400 metres and 1,500 metres freestyle double in London, but has courted controversy several times since.
In 2013 he found himself in hot water with Chinese swimming officials for missing training sessions and was suspended from engaging in any commercial activities, which had flooded in following his Olympic success.
He then fell foul of the law and spent a week in jail for crashing a car that he had driven without a licence.
In 2014, it emerged that Sun had secretly served a three-month ban after testing positive for a banned stimulant.
China could have imposed a longer suspension but opted for a lenient punishment because Sun had been given medication, which had only just been added to the banned list, to treat a heart issue.
Marculescu, in Singapore for the world junior championships, also said no action would be taken against Mexico for entering the wrong times for some of their swimmers in Kazan.
Marculescu said there were no rules to punish countries who falsified entry times and he did not consider the matter serious because none of the nation’s swimmers made it past the heats.
“No entry time or entry time, it’s not a big issue,” he said.
“There’s no rules to tell I have to punish him. He swims but he (doesn’t) qualify (for finals).
“He’s welcome to swim at the championships. It’s not so strict as the Olympics.”
(Reporting by Julian Linden; Editing by Neville Dalton)