Paul Wellens is the second Great Britain player following scrum-half Paul Deacon to be ruled out for the rest of the Gillette Tri-Nations, leaving his side without a specialist full-back to face Australia at Hull on Saturday.
The knee injury Wellens sustained in Saturday's record 38-12 win over New Zealand, which rekindled final aspirations, is more severe than at first thought. Either Leon Pryce or Richard Horne is expected to deputise against the world champions.
Great Britain could have summoned Richard Mathers, the Leeds Rhinos full-back who played against New Zealand a fortnight ago. However, coach Brian Noble will pin his faith in the current squad, though there is still a possibility of Gareth Raynor and Mark Calderwood making Test debuts on the wing.
Brian Carney, who suffered a hamstring injury on Saturday, has been able to train but his selection could be a gamble.
Bad luck has already prevented Wellens adding to his 12 Test caps, with a fractured cheekbone ruling him out of the 2002 drawn series against New Zealand and then tonsillitis sidelining him from the 3-0 Ashes defeat 12 months later. But when Kris Radlinski became unavailable this year Wellens proved the logical replacement and he was back to his best on Saturday.
Assistant coach Jon Sharp said: "Paul has damaged medial ligaments and is awaiting the results of scans and X-rays. It's a big blow for Paul and the team because he's an experienced player who has been very impressive."
St Helens-bound Pryce has won all his nine Test caps as a winger but started 10 matches for Bradford at full-back this year and will be favourite to take over from Wellens.
Horne, 23, moved from scrum-half, where he had replaced Deacon, when Wellens was injured and is certain to be in the 17-strong squad at his home ground.
"I knew that Paul Deacon, Iestyn Harris and Rob Burrow were ahead of me for a half-back spot this time because they had peaked at the end of the season, but I just had to be patient. I'm ready if needed," Horne said.
Brian McClennan, the New Zealand coach, is "80 per cent confident" the Kiwis will reach the Tri-Nations final at Elland Road on Saturday week. "We deserve to be there on the form we showed in our first three games," he said.
Great Britain will be eliminated if they fail to win by more than two points, but the Kiwis will be out if the home side win by between three and eight. A Lions victory by more than eight points will oust Australia.