South Korea's fading poster boy Park Tae-hwan insisted he wasn't about to retire as he announced his withdrawal from next month's Asian Games, saying he wasn't in good enough shape despite non-stop training.

The 28-year-old former Olympic champion, who has laboured to recover from a doping ban imposed in 2015, said he needed time to consider his future.

"Even if I have been training non-stop since 2016, I recently came to realise I am not in a good shape to achieve good results," Park said in a statement released by his agency.

"I and my company, therefore, have decided to stay away from the Asian Games," he said.

Park, nicknamed "Marine Boy", became Asia's first Olympic champion in the men's 400m freestyle when he took gold in Beijing in 2008.

Park, also South Korea's first Olympic swimming medallist, won the 100m, 200m, 400m and 1,500m freestyle at the national Asian Games trials in April.

"I'm not considering retirement yet but I'd like to have time to think about the future course of my activities," he said.

Park won a silver and five bronze medals at the 2014 Asian Games in Incheon, where the swimming competition was held at the Park Tae-hwan Aquatics Center.

But he was stripped of those medals and banned for 18 months after testing positive for an anabolic steroid in out-of-competition controls before the Games.

After the ban was lifted, Park entered three events at the 2016 Rio Olympics but was eliminated in the preliminary rounds, failing to add to his career tally of four Olympic medals.

Park also swept the gold medals in the 200m, 400m and 1,500m freestyle at the 2006 Asian Games, and won the 100m, 200m and 400m freestyle at the 2010 Asian Games.