The first two races of the MotoGP season have been cancelled due to the coronavirus outbreak.
The first race in Qatar on Sunday is off because of travel restrictions imposed on passengers from Italy.
Six of the riders in MotoGP's premier class are Italians and some teams are based in the country.
Organisers have now cancelled the second race in Thailand on 22 March "in the best interests of the nation and participants".
Moto2 and Moto3 will still race this weekend as their teams were already in Qatar for pre-season testing.
Speaking about the decision to cancel the Qatar event, a MotoGP statement said: "Italy clearly plays a vital role in the championship and in the MotoGP class - both on track and off - and therefore the decision has been taken to cancel premier class competition."
Seven-time world champion Valentino Rossi said news of the cancellations was "tough to take", especially as the next race is not now scheduled until 6 April in Texas.
"After a winter spent training, we were ready to start the season, both physically and psychologically," he said. "After the test in Qatar I really wanted to start with the first race.
"The MotoGP class cancellation for Qatar is difficult news to take because now we do not know how long we will have to wait before we can start racing.
"It's certainly a long time, considering the next GP in Thailand has been postponed for all classes. I hope everything will get better in the next weeks."
Globally, around 86,000 people have been infected with coronavirus - the vast majority in China's Hubei province, where the outbreak originated in December. Italy is the worst-hit country in Europe, with its death toll standing at 34 from around 1,700 confirmed cases.
Eleven towns in northern Italy at the centre of the outbreak - home to a total of 55,000 people - have been quarantined. Schools, universities and cinemas have been closed and several public events cancelled.
Several Serie A football matches were postponed this weekend, while fans from Atalanta - who are based in the northern Italian city of Bergamo, which has had deaths from the virus - were screened for symptoms as they came into the stadium before their win at Lecce on Sunday.
"The ongoing coronavirus outbreak has resulted in Qatar travel restrictions being brought into force that affect passengers from Italy, amongst other countries," MotoGP's statement added.
"As of today [Sunday], all passengers arriving at Doha on direct flights from Italy, or having been in Italy in the past two weeks, will be taken straight to quarantine for a minimum of 14 days."
F1's Australian Grand Prix going ahead
Meanwhile, the first race of the 2020 Formula 1 season in Australia next week is to go ahead as planned, with organisers saying "robust health, safety and emergency management arrangements" are in place to deal with the coronavirus outbreak.
The event is scheduled to take place in Melbourne from 12 to 15 March.
Organisers also say that ticket sales are up despite fears over the spread of the virus, with more than 320,000 expected to attend over the four days.
"At this stage there is no indication of further travel bans, nor is there any indication that Formula 1 and the teams will not be arriving as usual," added Australian Grand Prix Corporation chief executive, Andrew Westacott.