London - Mako Vunipola has been ruled out of England's Six Nations international against Wales this weekend after going into self-isolation as a precaution against the spread of the coronavirus.
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England's governing Rugby Football Union stressed that the Saracens prop was "not sick", with the 29-year-old Vunipola understood to have flown back from Tonga via Hong Kong.
Vunipola was included in a 34-man training squad named by England coach Eddie Jones on Monday for Saturday's match against Wales at Twickenham after recently travelling to Tonga for unspecified personal reasons.
But a RFU spokesperson said Tuesday: "Mako is not in camp on medical grounds. He is not sick, but it is a precaution.
Vunipola's absence means Joe Marler and Ellis Genge will compete to be the starting loosehead prop against reigning Grand Slam champions Wales
"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," said England forwards Matt Proudfoot earlier on Tuesday.
"We will give the guys a go who were there. Mako is a world-class player, but the guys have been doing a great job."
Both Jones and Wales counterpart Wayne Pivac are due to name their teams for the latest Anglo-Welsh clash on Thursday.
France are the only team left in the 2020 Six Nations that can complete a Grand Slam.
But World Cup finalists England haven't lost since being beaten by the French in their tournament opener and remain in title contention.
Wales, in their first season under Pivac after he succeeded fellow New Zealander Warren Gatland as coach following the World Cup, head to London looking to avoid a third straight loss having been defeated by Ireland and France.