The Italian, who missed two races at Spain's MotorLand Aragon circuit because of the virus, will take another test on Friday and only if he passes that will he be allowed to rejoin his team and compete.
Rossi has been in isolation at home in Italy after testing positive for the virus as recently as Tuesday. The 41-year-old is the first MotoGP rider to test positive for the new coronavirus.
American World Superbike rookie Garrett Gerloff is on standby if nine-times world champion Rossi is unable to race. (Reporting by Alan Baldwin in London, editing by Ed Osmond)