England prop Mako Vunipola has been quarantined over coronavirus fears.
Vunipola was yesterday named in England's 34-man squad but the Rugby Football Union said he did not come into camp after travelling through Hong Kong on his return from Tonga over the weekend.
Vunipola's self-isolation has been described as a precautionary measure but the recommended 14-day quarantine period leaves him unlikely to take any further part in England's scheduled Six Nations matches against Wales and Italy.
Vunipola missed England's dominant victory over Ireland 10 days ago after flying to Tonga for family reasons. His return flight took him through virus-hit Hong Kong, and he has now gone into isolation.
Vunipola is not believed to have shown any symptoms of the illness.
Ahead of their match against Wales at Twickenham this weekend, England forwards coach Matt Proudfoot said: "Mako is not with us now. He has got a medical issue so he won't be available for the weekend. It is just something medical so he is out for the weekend.
"We were excited to have him back, he is a great presence and a very experienced player, but we have great depth in our looseheads and they have been playing well.
"It is a medical issue, between him and the doctor."
An RFU spokeswoman added: "Mako is not in camp on medical grounds. He is not sick, but it is a precaution."
The Six Nations has already seen Ireland's game against Italy on Sunday (NZT) in Dublin cancelled due to coronavirus, with the Irish government unhappy due to the outbreak in northern Italy, while there is doubt over whether England's game in Rome next weekend will proceed.
On Monday tournament bosses confirmed that "as things stands" all other scheduled matches were set to go ahead.
Their statement read: "Six Nations and its six unions and federations are following the situation very closely with their respective governments and relevant health authorities and will strictly follow any directive given that would impact sporting events."
According to the World Health Organisation, more than 90,000 coronavirus cases have been confirmed globally.
Hong Kong has experienced 101 cases, including two deaths.