Olympic champion Cesar Cielo was cleared to compete in the world championships yesterday after the Court of Arbitration for Sport upheld the Brazilian federation's decision to warn rather than ban him for a positive doping test.

The 24-year-old world champion and three teammates had tested positive for the banned diuretic furosemide in May but their national governing body (CBDA) decided against banning them.

Swimming's world governing body FINA appealed that decision to CAS, which dismissed the appeal following a hearing in Shanghai.

"The CAS Panel composed of Alan Sullivan QC, Olivier Carrard and Jeffrey Benz decided to dismiss the appeals filed by FINA against Cesar Cielo, Henrique Barbosa and Nicolas Dos Santos and to confirm the CBDA's decision concerning them," CAS said in a statement.

FINA had asked for three-month suspensions to be imposed on Cielo, Santos and Barbosa and for one year against Vinicius Waked, who had been banned previously.

"The panel upheld the appeal by FINA against Vinicius Waked and sanctioned the athlete with a one-year suspension, as a result of a second doping offense," CAS said.

Waked had been banned for two months on February 4, 2010, following a positive test for a specified substance, CAS said.

Cielo, who won gold in the 50 and 100 meters freestyle at the 2009 Rome world championships and is the Olympic 50-meter freestyle champion, said the positive test had been caused by a supplement he took regularly that had become contaminated.

All four were training at the main pool in Shanghai yesterday.

The main swimming competition begins on Sunday.