Nick Easter
Nick Easter captained England in 2011 and returns to the international scene with his country in dire straits Getty Images

England have called up Nick Easter to replace Billy Vunipola for the remainder of the Rugby World Cup after the Saracens back-row was ruled out of the tournament with a knee injury. Vunipola was replaced during the second half of the 25-28 defeat to Wales and subsequent scans have shown he has strained ligaments, bringing a premature end to his participation.

Easter, a member of the World Cup squads in 2007 and 2011, was included in the original training squad announced in May and was in contention to be included in the 31-man group until being dropped at the last minute. The 37-year-old was suffering with a back problem in the summer but having fully recovered the Harlequins man has been parachuted into the squad in an attempt to resuscitate England's campaign.

"It's unfortunate for Billy but the scan shows an injury that will likely require up to six weeks recovery," coach Stuart Lancaster said. "He has worked really hard and committed everything to the last three months but he is a young man with a bright future ahead of him and he will be an integral part of this team for years to come. Nick was unlucky to miss out on final selection. He is a specialist number eight and an experienced player and we know he will make a big contribution."

Lancaster will confirm his team for the crunch Pool A match against Australia on 1 October and is expected to ring the changes due to four further injury concerns. Ben Youngs and Courtney Lawes – who both featured against Wales – as well as Ben Morgan and Jonathan Joseph are all fitness doubts and it waits to be seen whether the England coach's alterations will be born out of necessity or design. Tom Wood is available though after escaping punishment for kicking Liam Williams.

Meanwhile, despite having a five-day turnaround after the heroics at Twickenham, Wales have made just three changes for their next pool match against Fiji, where a bonus point victory would see Warren Gatland's side take a giant step towards the last eight. The changes are all enforced after Scott Williams and Hallam Amos were both ruled out of the rest of the tournament with knee and shoulder injuries, while the concussed Williams will also be absent as he continues to be assessed after being taken off against England.

The trio are replaced by Matthew Morgan, Alex Cuthbert and Tyler Morgan for the match at the Millennium Stadium, but Wales are unchanged elsewhere with Dan Biggar, fresh from his match-winning penalty, starting alongside try-scorer Gareth Davies at half-back. "It is important we build on the success and momentum from last weekend and take that into Thursday," Gatland said.

"Fiji have performed very well in their opening two games and they will be coming to Cardiff looking to build on that themselves. We have made three changes through injury but go into this game with a strong side. We are looking forward to being back at the Millennium Stadium on Thursday and having the crowd right behind us in an important World Cup fixture."

Wales: 15. Matthew Morgan, 14. Alex Cuthbert, 13. Tyler Morgan, 12. Jamie Roberts, 11. George North, 10. Dan Biggar, 9. Gareth Davies, 1. Gethin Jenkins, 2. Scott Baldwin, 3. Tom Francis, 4. Bradley Davies, 5. Alun Wyn Jones, 6. Dan Lydiate, 7. Sam Warburton, 8. Taulupe Faletau

Replacements: 16. Ken Owens, 17. Aaron Jarvis, 18. Samson Lee, 19. Luke Charteris, 20. Justin Tipuric, 21. Lloyd Williams, 22. Rhys Priestland, 23. James Hook.

More about Rugby World Cup 2015