Olympic champion Cesar Cielo is expected to find out by tomorrow whether he will be banned from swimming, after the Court of Arbitration for Sport held a special six-hour hearing yesterday into the Brazilian's doping case.

The CAS panel was specially assembled to deliver a verdict in the case before Cielo is scheduled to compete in the freestyle relay on Sunday at the world championships.

Cielo is also hoping to defend his world titles in the 50 and 100 free, plus he is entered in the 50 butterfly.

Swimming's governing body FINA challenged a Brazilian federation decision to give Cielo only a warning after he tested positive for furosemide, a banned diuretic and masking agent, at a meet in Rio de Janeiro in May.

Cielo said he consumed the drug in a contaminated batch of a food supplement he regularly used. He could face a ban of two years under WADA rules.

Three other Brazilian swimmers - Nicholas Santos, Henrique Barbosa and Vinicius Waked - also tested positive for furosemide and were let off with warnings by their national federation. Waked has previously served a two-month ban for a separate doping offense.

All four swimmers attended yesterday's hearing at the Shanghai University of Political Science and Law, although only Cielo has qualified to compete at worlds.

"I can see when there is real doping and this is not, for sure," said Sandre Soldao of the Brazilian anti-doping agency, a former Olympic triathlete who attended the hearing. "There is a problem in the supplements industry. Everyone in sports medicine knows about this - 30 percent of supplements are contaminated with something and that's a real problem.

"All athletes use supplements these days. For me it's very clear."

The Brazilian anti-doping agency sends all of its samples to a Montreal lab for testing, and that's where the positive tests were first reported, according to Soldao.

The Brazilian lab then tested the supplements provided by the athletes and found traces of furosemide, according to Soldao.