Hendre Fourie is on standby to start for England against Ireland - just five days after being omitted from Martin Johnson's World Cup squad.
The Sale flanker has joined up with England in Dublin as emergency cover after number eight Nick Easter and flanker Tom Wood both suffered calf injuries.
Easter will undergo a fitness test on a "tight calf" on Saturday morning - but England will not risk one of their senior players in a warm-up international with the World Cup just a fortnight away.
Wood has already been replaced on the bench by Stade Francais lock Tom Palmer after suffering what England manager Johnson described as a mild calf strain.
If Easter is withdrawn then Fourie - left out of England's 30-man World Cup squad on Monday - will go straight into the team at openside flanker with James Haskell switching to number eight.
With England's resources stretched, starting lock Courtney Lawes will be called upon to provide the back-row cover.
Johnson has been forced to call on Fourie after naming only five specialist back-row forwards for the World Cup, including his injured captain Lewis Moody.
The Bath flanker has remained at England's Pennyhill Park base this weekend to work on his rehabilitation but Johnson confirmed he would fly to New Zealand with the squad on Monday.
The England medics insist Moody, who is recovering from knee ligament damage, is on course to be fit for the opening World Cup clash with Argentina on September 10.
Johnson views the Ireland game as the perfect launch-pad for England's campaign in New Zealand, which begins against Argentina on September 10.