Mako Vunipola is unavailable for England's crunch Six Nations clash against Wales.
Saracens prop Vunipola was absent for England's win over Ireland last time out as he was in Tonga for family reasons.
While Vunipola was named in a 34-man squad on Monday to prepare for Wales at Twickenham, he will now not be involved in the fixture due to a medical problem.
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Speaking to Sky Sports, England's forwards coach Matt Proudfoot said: "He's not with us due to medical reasons.
"I won't say injury, it's medical reasons, yeah [he's unavailable]."
Wales, meanwhile, confirmed Amos is to undergo surgery on a knee injury sustained playing in Cardiff Blues' Pro14 victory over Benetton Treviso on February 23.
A Welsh Rugby Union statement revealed it is expected that the wing will also miss the remainder of the campaign.