A damaging drugs scandal overhangs the world swimming championships in Shanghai, where a misfiring Michael Phelps will try to reignite his Olympic form as the countdown begins to London 2012. Phelps is expected to compete in up to seven events at the purpose-built Oriental Sports Centre on the city\'s outskirts, a state-of-the-art facility which will host 16 days of swimming, diving and water polo from Saturday. But an unsavoury doping episode has dragged the media spotlight away from the US phenomenon and on to beleaguered Brazilian star Cesar Cielo, whose fate hangs in the balance after testing positive for a banned diuretic. World swimming chiefs appealed after Brazilian officials let the 50m Olympic champion and world record-holder off with just a warning. The Court of Arbitration for Sport (CAS) has promised to deliver a quick verdict. Cielo, 24, blames a contaminated food supplement for the positive test. But the incident, dubbed \"bad for world swimming\" by French rival Alain Bernard, is poorly timed for the sport, coming on the eve of its biannual showpiece. Swimming is also desperate to move on from the embarrassing high-tech swimsuits era, when polyurethane-clad athletes set a swathe of super-fast world records which are virtually untouched since the clothing was banned last year. Two years ago in Rome, a staggering 43 world bests fell in scenes of near-farce which badly dented swimming\'s integrity. In Shanghai, only a handful of new global bests are expected. \"The 2009 World Championships were a joke with the more than 40 world records,\" Swimming World Magazine\'s John Long told AFP. \"None of that was pure. But we\'ve moved on and the sport is where it should be these days, based on talent and work ethic.\" Phelps, now 26, managed five golds in Rome, even without a super-suit. But he will be looking to banish some patchy performances as the clock ticks down to London\'s Olympics next year. The Baltimore Bullet, who tore up the record books with eight gold medals at the 2008 Beijing Olympics, has suffered a number of shocks this season -- including finishing sixth in the Charlotte UltraSwim 200m free in May. He admitted he needed to work harder in training and was looking for extra confidence after honing his preparations with two victories at this month\'s Canada Cup. \"I\'m really happy with that and I know I need to do more training,\" said Phelps. \"It\'s races like these that I think help me more mentally than anything else. \"Being able to still see that I can pop a good race here and there gives me a little bit of a confidence.\" China will build on their third place in Rome as they host their first world championships, led by Sun Yang, women\'s 200m butterfly Olympic champion Liu Zige and women\'s 50m backstroke world champion Zhao Jing. Sun, 19, is expected to test Grant Hackett\'s long-standing 1,500m world record, and his 400m freestyle duel with South Korean rival Park Tae-Hwan is tipped as one of the events of the tournament. Australia will hope to bounce back from their disappointing 2009 showing, where they placed fifth, led by their three women\'s world champions and triple Olympic gold-medallist Stephanie Rice. \"We won four in Rome in 2009 which was a disappointing performance, and we certainly want to exceed that total (in Shanghai) without giving a number,\" head coach Leigh Nugent said. \"Shanghai will put on a fantastic world championships and this will be the first time since Rome in 2009 that the best in the world will all be swimming in the same pool, at the same time,\" Nugent added. China will dominate the diving events, which start on Saturday, and Russia are expected to maintain their stranglehold on synchronised swimming after winning every category they entered in 2009.