WHO spokesman Roy Wadia said Tuck-Weng kok, an Australian expert, arrived in Beijing on Monday.
"He will be staying in Beijing where he will do an extensive review of the tests that have been done so far on the suspected SARS case," Wadia said.
China announced the discovery of the suspected case on Saturday, but a battery of tests on the 32-year-old man has so far been unable to conclusively confirm he has SARS.
Meanwhile, a four-member WHO team is en route to Guangzhou, capital of Guangdong province, to work with health ministry experts on further examining the patient and verifying test results.
The patient, a freelance journalist identified only as Luo, developed a fever on 16 December and was taken to hospital with pneumonia in the right lung on 20 December.
China was the country worst affected by the SARS epidemic that first struck southern Guangdong in November last year, and went on to infect 5327 people nationwide, killing 349.
The disease travelled across the globe, causing 774 deaths from more than 8000 infections, the vast majority in Asia.
Scientists believe SARS is caused by the Corona virus, which also causes the common cold.
Known symptoms are similar to those of flu, including high fever, headaches, sore throats, and coughs.
At the moment there is no vaccine for the disease.