Lions flanker Lewis Moody faces a race against time to be fit for first Test contention against New Zealand next week.
The Leicester forward has withdrawn from his place on the bench for Wednesday's clash against Wellington, when he will be replaced by his England colleague Richard Hill.
The Lions confirmed Moody had suffered an injury to his left knee in training, but the apparent seriousness was not revealed until coach Gareth Jenkins spoke to the media in Wellington on Tuesday.
Jenkins revealed that Moody is "out of the selection process" for next Saturday's game against Otago in Dunedin, and that will seriously hamper his Test prospects, given the Lions boss Sir Clive Woodward is likely to have finalised his first choice line-up by early next week.
Moody has not travelled to Wellington, remaining behind at the squad's Christchurch base for further tests.
Three players - Lawrence Dallaglio, Malcolm O'Kelly and Simon Taylor - have already been ruled out of the tour because of injuries.
The possible loss of Moody would be a huge blow, given his versatility at blindside and openside flanker, but it would appear the signs are not good.
Prop Andrew Sheridan, meanwhile, is battling to overcome an ankle injury sustained against the New Zealand Maori last Saturday, raising doubts about his prospects of being fit to face Otago. Like Moody, Sheridan is a serious candidate for the Lions' Test 22.
The British and Irish Lions team to play Wellington on Wednesday is:
J Lewsey (Wasps and England); J Robinson (Sale and England), B O'Driscoll (Leinster and Ireland, capt), G Henson (Ospreys and Wales), G Thomas (Toulouse and Wales); J Wilkinson (Newcastle and England), D Peel (Lanelli and Wales); G Jenkins (Cardiff and Wales), S Byrne (Leinster and Ireland), J White (Leicester and England), D Grewcock (Bath and England), B Kay (Leicester and England), S Easterby (Llanelli and Ireland), N Back (Leicester and England), M Corry (Leicester and England).
Replacements: G Bulloch (Leeds and Scotland), M Stevens (Bath and England), P O'Connell (Munster and Ireland), R Hill (Saracens and England), C Cusiter (Borders and Scotland), S Jones (Clermont Auvergne and Wales), S Horgan (Leinster and Ireland)
As Gloucester prepare for their 39th game of the season, against Bordeaux-Begles at Sixways on Sunday, David Humphreys told the local media that this week has been all about getting the players mentally and physically ready after a tough game against Connacht last Sunday.
Speaking to GRTV after the 40-32 victory over Connacht on Sunday, skipper Billy Twelvetrees explained that Gloucester had had to learn to be patient and cut out the errors to earn the win and progress to next weekend's final play-off against Bordeaux-Begles.
Jonny May's superb late score capped a thrilling 40-32 European play-off win over Connacht on Sunday. The winger spoke afterwards of his team's character and spirit as he looked ahead to one more week of rugby.
Speaking to GRTV this afternoon, Director of Rugby David Humphreys hailed the 'never say die' attitude of the team, after despite not being at their best, fighting back to take a 40-32 win after extra time over Connacht.
Jonny May continues on the wing on Sunday as Connacht come to town, and the England wing explains to the local media this week that he is delighted with his form and is looking forward to taking on Pat Lam's men.
Premiership Rugby have this morning confirmed the order of fixtures for the 2015/16 season, and Gloucester Rugby will start their campaign at Kingston Park, taking on Newcastle Falcons on Friday 16 October, 19:45.