Cielo's case will be heard next Wednesday by the Court of for Sport, four days before the swimming portion of the championships open.

The worlds open with diving women's 3-meter synchro and men's 1-meter springboard preliminaries Saturday.

Swimming's governing body FINA challenged a Brazilian federation decision to give Cielo and three teammates only a warning after he tested positive in May for furosemide, a banned diuretic, and blamed it on a contaminated batch of a food supplement Cielo regularly used.

The CAS hearing will be held in Shanghai.

"We made the appeal because the information was incomplete," FINA executive director Cornel Marculescu said on Friday, indicating that Cielo's explanation needs to be examined more thoroughly.

Cielo swept the signature sprinting events — the 50- and 100-meter freestyle — at the last worlds in Rome two years ago. He also took gold in the 50 free at the 2008 Beijing Olympics.

Cielo could face a ban of two years under World Anti-Doping Agency rules. And if he's banned for more than six months, the Brazilian could be excluded from defending his Olympic title at the 2012 London Games under existing International Olympic Committee rules.

Marculescu wouldn't say what type of decision would satisfy FINA.

"It's not about what we want. It's a juridical issue that depends on the laws," Marculescu said. "We just want what's right." At the CAS hearing in Shanghai, Cielo will be represented by Los Angeles attorney Howard Jacobs, while FINA is flying in from Switzerland its lawyer specializing in doping cases, Jean-Pierre Morand.

Jacobs previously represented American swimmer Jessica Hardy in a similar case: Hardy withdrew from the US team ahead of the Beijing Games and was later ordered to serve a one-year ban despite the CAS accepting that she was not at fault for a contaminated dietary supplement.

Meanwhile, Brazilian swimming federation president Nunes Filho is staying silent.

"After the (decision) I'll talk with the press," Nunes Filho said. "Please respect that." So what does four-time Olympic champion swimmer Alexander Popov, a member of the IOC's athletes' commission and a former sprinter, think? His response was similar to Nunes Filho's: "Making any (comment) would be inappropriate for now," Popov said.