Mako Vunipola's absence for England's Six Nations clash against Wales is because he is in self-isolation as a precaution against the coronavirus, the Rugby Football Union (RFU) has confirmed.
The powerhouse prop was named in a 34-man squad for the Twickenham encounter but was ruled out by forwards coach Matt Proudfoot on "medical reasons" on Wednesday.
It was later confirmed Vunipola did not come into camp as he travelled back from Tonga via Hong Kong at the weekend.
An RFU spokesperson said: "Mako is not in camp on medical grounds. He is not sick but it is a precaution."
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Vunipola was missing from England's superb victory over Ireland last time out as he travelled to Tonga for family reasons.
Travellers who have been in areas where the coronavirus has been prevalent have been advised to self-isolate, meaning Vunipola may also be a doubt for England's Six Nations sign-off against Italy on March 14.
Six Nations organisers said this week the intention is for all fixtures to be completed, with Ireland's Dublin contest against Italy, which was due to take place this weekend, having been postponed.