England could be missing a Vunipola
England could be missing a VunipolaSHARE
The back row forward may now be unable to train until Thursday at the earliest, after suffering the injury during England's 37-21 win over South Africa at Twickenham last Saturday.
His clash of heads with South Africa's Eben Etzebeth forced the Springbok lock to go off before half-time.
Etzebeth was ruled out Monday of South Africa's match against Italy this weekend with concussion, but England officials stressed that Saracens No.8 Vunipola had not suffered a head injury.
An update on Vunipola's fitness is expected on Wednesday, with the Fiji-born Nathan Hughes set to take his place if he is unavailable for a match where England will look to extend their winning streak to 12 in a row and make it 11 victories out of 11 under Australian coach Eddie Jones.
Hughes won his first cap of the bench against South Africa, with prop Kyle Sinckler and centre Ben Te'o also making their Test debuts after coming on as replacements.
"They did really well and it improves the competitiveness in our squad, making selection harder, which is what Eddie wants," said England forwards coach Steve Borthwick on Monday.
"All three players bring a lot of power and explosiveness to the field."
Definitely ruled out of facing Fiji is Dave Attwood, who managed to sustain a knee injury in the 10 minutes the Bath lock was on as a replacement for World Player of the Year nominee Vunipola at the end of the South Africa match.
"We've got a few bumps and bruises from Saturday," said former England captain Borthwick.
"Dave Attwood is having his knee treated. He's having an injection on his knee and is then returning to Bath, so is unavailable."