In March, China's state media had reported that six athletes have failed doping tests

Chinese athletes had failed doping tests -- including two who were let off with warnings for taking the banned muscle-builder clenbuterol.

Liu Peng, head of the General Administration of Sport, said in May that WADA's suspension of the Beijing lab has brought "difficulties and challenges" for China's anti-doping work, according to a Chinese media report.

Chinese swimming has a chequered reputation following a rash of doping cases in the 1990s. Seven Chinese swimmers tested positive for steroids at the 1994 Asian Games in Hiroshima.

In 1998, swimmer Yuan Yuan was banned after Australian customs officers discovered a large stash of human growth hormone in her bags at the world championships in Perth.

The towering Sun will be the most recognisable figure in China's team, but his current form is largely an unknown quantity after he missed the national championships in April with a foot injury.

In June at Santa Clara, he won the 200m freestyle in a world-leading time, but then pulled out of the 400m final and the 1500m event without explanation.

It echoed last year's world championships in Kazan, Russia, where Sun won the 400m and 800m but withdrew from the 1500m, blaming a heart condition.

Kazan was eventful for Sun, who was also involved in an angry confrontation with Brazil's Larissa Oliveira in the warm-up pool.

Sun will hope for less choppy waters in Rio -- although he may face a challenge from Italy's Gregorio Paltrinieri, who swam the second-fastest 1500m in history at the European championships in May.

As for Ye, after her phenomenal 2012 Olympics, she failed to make the podium at either the 2013 or 2015 world championships, and was 22 seconds off her 400m medley world record at the Chinese championships, after suffering stomach pain.

However, Ning Zetao, who served a one-year suspension after testing positive for clenbuterol in 2011, should shine for China after he upstaged a strong field to win 100m freestyle gold at last year's world championships.

PTI