But Olympic champion runner Sebastian Coe, a vice president of track and field's ruling body, said Tuesday the competition is bigger than any individual athlete.
"We will have here in Moscow some of the world's greatest competitors, both domestically and internationally," Coe said. "And the message that should emanate from the last few weeks is that the IAAF (and others) take the abuse of drugs in sport very, very seriously."
The worlds start Aug. 10 and last nine days, and Powell and Gay won't be there.
"The message is very clear: If you choose to cheat, the technology is there and the will within the IAAF and within the international federations and the national governing bodies is there to make sure that our sport is clean and is competed all with integrity," Coe said.
Also, the organizing committee said authorities have taken all necessary security measures to keep the competition safe.
"We hope that our law enforcement agencies do a perfect job," said Alexei Vorobyev, the head of Moscow's sports department.