England's buccaneering No 8 Billy Vunipola has been forced out of the World Cup with a knee injury to be replaced by evergreen Nick Easter

Billy Vunipola has become the latest high-profile player to withdraw from the World Cup through injury, following the likes of Jean de Villiers, Yoann Huget, Grant Gilchrist and Scott Williams, with the age-defying 37-year-old Nick Easter called up in his place.

Vunipola had to leave the field with 18 minutes remaining of Saturday’s dramatic defeat to Wales, straining knee ligaments that are expected to keep him out of action for six weeks.

As a result, his first World Cup is already over, and it remains to be seen whether his bonus-point try in the final minutes against Fiji on the opening night will prove to be relevant in the final shakeup in Pool A.

Nick Easter

Easter option: Nick Easter will bring leadership and skill to the England backrow

With leadership lacking on Saturday, Stuart Lancaster has gone with the pragmatic choice in Easter, who will be desperate to improve on his last World Cup contribution, which ended with the infamous ‘that’s £35k down the toilet’ quote.

The question now though, is what does Lancaster do on Saturday in England’s make-or-break clash with Australia at Twickenham? One positive is the fitness of Ben Morgan, who missed the Wales loss through injury, and could be parachuted straight back into the team.

From a tactical standpoint, Morgan is England’s closest imitation of Vunipola, with his own powerful carrying game, while also being one of the better options on the deck. That will be vital against the Australians, with England already looking overmatched at the breakdown against the combination of David Pocock and Michael Hooper.

David Pocock

Double-trouble: Michael Hooper and David Pocock will cause any teams trouble at the breakdown

However with Morgan only just back from an injury of his own, he will need to prove that he is up to speed, with Easter in a similar boat having not played since being cut from the squad at the end of August and last been seen giving pitchside analysis during the World Cup.

A number of former players have already suggested that Easter should come straight into the starting lineup, and his offloading ability would certainly come in very handy. In that regard, he is even more proficient than Vunipola, having finished top of the offloading charts in the Premiership last season.

However a start for Easter would mean yet another change of tact for Lancaster, who has always favoured a big ball-carrier at number eight. The last time one of Vunipola or Morgan didn’t start there for England was back in 2013 and a certain unmentionable game in Cardiff with Tom Wood filling in.

Ben Morgan

Step up: Ben Morgan is widely expected to fill the No 8 berth

With that in mind, Morgan seems more likely to start and when fit, he has been very useful for England. Still, Vunipola will be a loss, after one of his best performances of the year against Wales prior to injury.

The Saracens back rower topped the charts for metres made against the Welsh, and was visibly more effective than James Haskell who replaced him. Saturday will tell us whether England can find a solution to replace him while they are still in with a shout of escaping the pool stages.