Danny Care has emerged as an injury doubt for Saturday's first Test against New Zealand in a potentially damaging blow to England's prospects of upsetting the All Blacks.
Care, the catalyst behind England's improved attacking game in the most recent RBS 6 Nations, jarred his shoulder after suffering an accidental fall in training.
The Harlequins scrum-half will be given until Thursday night to prove his fitness with Ben Youngs starting in his place if he fails to recover.
It is another alarming development for England, whose preparations for the series opener in Auckland have been undermined by an ever-lengthening injury list.
Adding to head coach Stuart Lancaster's problems is the absence of any further scrum-half cover among the first wave of players who arrived in Auckland last week.
If Care is ruled out, a jet-lagged Lee Dickson will be picked on the bench just three days after landing in New Zealand and seven days after helping Northampton to the Aviva Premiership title.
"Danny is a concern and I'll give him until the captain's run on Friday," Lancaster said.
"At the moment we're hoping he'll be fine for the game, but it's meant I've had to put Lee Dickson on standby. It's not ideal but needs must."
Care's 47 international appearances make him the second most-capped player in the 23 picked to face New Zealand. Given the inexperience of Freddie Burns and Kyle Eastmond outside him, England can ill afford to lose a half-back of his quality.
Leicester-bound Burns has been preferred ahead of Danny Cipriani at fly-half, despite enduring a dismal season at Gloucester, and Eastmond profits from the ankle injury that has accounted for Billy Twelvetrees.
Eastmond, a rugby league convert, impressed during last summer's tour to Argentina where he won both of his caps, but has fallen out of favour at Bath and has not played since April 27.
The 10-12 channel is the obvious weak link in the team as Eastmond and Burns are each fourth choice in their positions.
"We're going to be tested there, there's no doubt about it," Lancaster said.
"Kyle didn't get picked towards the end of the season but he was exceptional in Argentina and every time he's trained with us. We've seen huge potential in him.
"The partnership of him and Manu Tuilagi has looked promising in training. Freddie's been training well so as a midfield partnership, it's nicely balanced.
"It's still got that ball playing 12 that I prefer to have and someone to distribute and make good decisions and it's got the power runners as well.
"Clearly for us we need to give Kyle the licence to do what he does best and that's put people through holes, but also encourage him to take on players himself as he's a genuine running threat and a passing threat."
The only two areas of debate in the pack have been settled with Geoff Parling's line-out expertise seeing him start ahead of Dave Attwood and the physicality of James Haskell being preferred to Tom Johnson.
The starting XV contains seven survivors from the victory over Italy in March and a total of 299 caps, but there is a worrying lack of firepower on the bench.
Lancaster, however, insists it is a 23 capable of denying the All Blacks a 15th successive victory.
"It's certainly a big challenge we're facing, but there'll be no excuses because the side we've got is an experienced and good one," he said.
"I certainly think we need to earn the respect of the All Blacks, not just as a group of players but as a nation and that will only happen at the end of the third Test. This is an important start."
England team to face New Zealand at Eden Park, Auckland, on Saturday June 7, 0835 KO BST:
M Brown (Harlequins); M Yarde (Harlequins), M Tuilagi, (Leicester Tigers), K Eastmond (Bath), J May (Gloucester); Freddie Burns (Leicester Tigers), D Care (Harlequins); J Marler (Harlequins), R Webber (Bath), D Wilson (Bath), J Launchbury (London Wasps), G Parling (Leicester Tigers), J Haskell (Wasps), C Robshaw (Harlequins, capt), B Morgan (Gloucester).
Replacements: J Gray (Harlequins), M Mullan (London Wasps), H Thomas (Sale Sharks), D Attwood (Bath), T Johnson (Exeter Chiefs), B Youngs (Leicester Tigers), D Cipriani (Sale Sharks), C Pennell (Worcester).