Along with teen phenomenon Ye Shiwen, beset by doping innuendo as she claimed two individual medley golds, China cemented their new position as the world’s number two team behind America.

But a falling-out between Sun and his coach over his love affair with a stewardess has rocked the Asian swimming power as it prepares for Barcelona.

Sun, the tall distance specialist from Zhejiang, rejected coach Zhu Zhigen’s demand that he stop seeing his new girlfriend and concentrate on his swimming instead.

Despite a public show of reconciliation with Zhu, Sun has been training in Hong Kong under former Chinese head coach Zhang Yadong, and it is unclear which events he will contest this month.

“Athletes want to get good results, and to do this you need systematic and scientific training without outside interference,” Sun complained on his official microblog.

“I was not able to do this in the past for various reasons, and have been making up ground through my own efforts.

“With the world championships approaching, I want to eliminate outside interference and prepare well, to give me added strength.”

Sun became the leading light of Chinese swimming when he tore up Grant Hackett’s 10-year-old 1500m record at the 2011 Shanghai world championships -- a mark he lowered again at the Olympics.

Sun also claimed the 800m world title in Shanghai but Chinese officials were unsure whether he will defend it this month - or swim any events at all - after he only signed up for the 1500m and 400m freestyle.

“Sun Yang only had two events registered. We are concerned that he is not able to perform well as he has lacked systematic training the past six months,” Chinese swimming’s deputy head Shang Xiutang told domestic media.

“We are even not so sure about these two events now.”

While attention will focus on Sun, 17-year-old Ye will also be in the spotlight as she tries to defend her 200m individual medley world title and again deflect the speculation that accompanied her feats in London.

Ye, then 16, raised eyebrows when she oblitreated the 400m medley world record with a sensational freestyle lap, timing faster over the final leg than men’s winner Ryan Lochte a few races earlier.

“I was very depressed and angry after London but everything is fine now,” she told Britain’s Independent last month.

“It is a long journey. Different people have their different views but I will just keep on going,” she added.

Asia’s other swimming nations have also faced problems and South Korea head to Spain without their most high-profile performer and only reigning world champion, Park Tae-Hwan.

Park, whose 400m freestyle gold at Beijing 2008 was South Korea’s first ever Olympic swim medal, was at the centre of controversy in London when he was disqualified from his title defence over a false start, before being reinstated and eventually finishing second.

But the “Marine Boy” has since lost his key sponsor, who reportedly judged the 23-year-old as past his peak, and has rowed with Korean officials, who refused to give him his prize money for his two silver medals in London.

Park, who has appeared on a home shopping channel to fund his training, skipped South Korea’s trials and will not defend his 400m world title, with China and Japan leading Asian hopes in the pool.

Japan’s “Frog King” Kosuke Kitajima, now 30, returns to the city where he set 100m and 200m breaststroke records at the 2003 world championships.

Akihiro Yamaguchi arrives as the reigning men’s 200m breaststroke world record-holder, while backstroker Ryosuke Irie will hope to improve on his bronze and silver medals in London.

Fellow Japanese Kosuke Hagino, 18, and Aya Terakawa, 28, also have Olympic pedigree after winning bronze medals in London in the men’s 400m individual medley and women’s 100m backstroke respectively.