( CNN ) -- Brazil 's Olympic swimming champion Cesar Cielo is free to compete in this year 's world championships after escaping a drugs ban . Cielo , who won the 50m freestyle at the 2008 Beijing Games , was cleared by a special tribunal of the Court of Arbitration of Sport sitting in Shanghai where the worlds are being held . Cielo and teammates Nicholas dos Santos and Henrique Barbosa were given warnings after testing positive for a banned diuretic . But another swimmer on the Brazilian squad , Vinicius Waked , was banned for a year because it was his second violation for drugs offences . The CAS tribunal dismissed an appeal by world swimming 's governing body FINA , who wanted stiffer punishments . It followed a six-hour hearing Wednesday at which Cielo appeared to give evidence . The quartet tested positive for Furosemide , which can act as a masking agent for other banned drugs , at a meeting back in May . They claimed that a caffeine supplement had been contaminated to bring about the failed drugs test . The decision to clear Cielo is a major boost for the world swimming championships where he is set to be a big attraction . But it drew criticism in some quarters and triple world champion Roland Schoeman wrote on his Twitter blog : `` FINA and the CAS have done a great disservice to the world of swimming & set a dangerous precedent . '' Cielo is reigning world champion over 50m and 100m , breaking the championship record in the shorter sprint and setting a new world mark of 46.91 seconds in the 100 in Rome two years ago . The 24-year-old is also the holder of the world record in the 50m , setting a record of 20.91 in Sao Paulo in December 2009 . American Michael Phelps , who won a record eight golds at the Beijing Olympics , returns to China for the competition and could swim up to seven events as he builds up to London 2012 .
Mexico 's Olympic swimming champion Cesar Cielo escapes drugs ban . Special Court of Court of Arbitration of Sport gives Cielo a warning . Cielo can defend his 50 and 100 m freestyle titles at the worlds . Cielo and two other swimmers tested positive for banned diuretic .