Tuliagi and Corbisiero set to both miss out.
England centre Manu Tuilagi will miss Saturday’s Six Nations opener against Scotland at Twickenham with an ankle injury.
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Meanwhile prop Alex Corbisiero has been ruled out of the entire championship with a knee problem.
Lancaster said England had “run out of time” to sort out Samoa-born Tuilagi’s ankle injury but he was confident the Leicester centre would be training fully next Tuesday or Wednesday.
Tuilagi’s loss is a blow to England ahead of this weekend’s Calcutta Cup clash as the powerful midfielder played a key role in their record-breaking 38-21 win over world champions New Zealand at Twickenham last time out in December, scoring one and helping create two of the team’s three tries.
“By the end of the week we expect Manu to be running fully and changing direction,” Lancaster said.
“The message I’m receiving from the medical team is that he will be training fully by Tuesday or Wednesday next week, but I’ll need to make a call earlier in the week. He won’t be training properly until at least Friday.
“Manu is a big loss — he was outstanding against New Zealand. But he missed the first two games of last year’s Six Nations because of a hamstring and it’s an opportunity for someone else.
“It’s disappointing for him, but it’s not a long-term injury so he’ll be back soon,” he added.
Now Lancaster, who in his debut tournament in charge of England led them to a runners-up spot in last season’s Six Nations, with their only defeat coming against Grand Slam champions Wales, is set to decide between the ball-playing Billy Twelvetrees and Jonathan Joseph as a midfielder partner for Brad Barritt.
“We have a pretty good idea of how we’ll rejig the midfield. We have our thoughts,” said Lancaster, due to name his team to play Scotland on Thursday.
“It changes the emphasis a little bit, but it won’t fundamentally affect the way we play,” he insisted ahead of the latest edition of rugby’s oldest international fixture.
“Brad will be in the equation and we need to make sure we can still break the gainline and have physical defenders. We’ve got to have the ability to get across the gainline and defend.”
Corbisiero damaged his knee during England’s tour of South Africa last year but returned to action only for the injury to cause problems again after he played in England’s stunning victory over the All Blacks.
“The reality is the surgeons recommended two weeks rest and said it would then take six to eight weeks to be back playing, so that will rule him out of the Six Nations,” said Lancaster.
“Hopefully he’ll be back around the final game against Wales (in Cardiff on March 16), but the reality is he’ll have to play two or three Premiership games first…Everyone’s positive and upbeat about his recovery.
“Alex is a big loss, but Joe Marler has played well for Harlequins recently. Mako Vunipola is improving all the time and Nick Wood was outstanding for the Saxons (England’s A or reserve team).”
Among England’s possible replacements, Gloucester fly-half Freddie Burns has been ruled out against Scotland and Ireland with a knee ligament injury, while Wasps No 8 Billy Vunipola is struggling with an ankle problem.
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