London - England face a selection headache at loosehead prop after British and Irish Lions star Alex Corbisiero was ruled out on Tuesday of Saturday's clash with world champions New Zealand because of a nagging knee injury.
The 25-year-old -- who played in two of the three Lions tests against Australia this year which saw the Lions win the series 2-1 -- has been struggling with a knee injury since he twisted it playing for his club Northampton last month.
Corbisiero -- born in New York but whose parents emigrated to England when he was four -- missed the opening test against Australia but played in the second-half of last Saturday's 24-12 win over Argentina.
Corbisiero joins fellow loosehead prop Mako Vunipola on the sidelines while there is a doubt over third choice Joe Marler, who was taken off at half-time on Saturday because of concussion.
That would leave England coach Stuart Lancaster looking at his fourth choice prop Matt Mullan as he bids to record a second successive win over the All Blacks at Twickenham.
Lancaster also lost wings Marland Yarde and Christian Wade on Tuesday, which relieved the pressure on under-fire veteran Chris Ashton.
"Alex took part in Tuesday morning's forwards training session but suffered some discomfort to his knee," Lancaster said.
"He did not train on Tuesday afternoon and will not be available for selection for the weekend.
"It's disappointing for Alex having missed last year's Six Nations because of an injury to his other knee.
"With Mako also unavailable, it's a great opportunity for Joe Marler and Matt Mullan, who has been with us all week and is raring to go in the 23."
Marler has undergone a daily increase in activity as demanded by concussion guidelines and is due to undergo a full contact session on Thursday, the day Lancaster names his team.
"Joe Marler has had no symptoms of concussion since Saturday," England team doctor Phil Batty said.
"He has passed all his cognitive function (CogSport) tests and balance assessments and completed a skills session on Tuesday without any problems."
Lancaster trimmed his squad to 23 players on Tuesday with tighthead prop, where Dan Cole and David Wilson are competing, the only likely change to the starting XV.