The British & Irish Lions have growing concerns over the fitness of George North and Manu Tuilagi before next week's first Test against Australia, with the head coach, Warren Gatland, also yet to confirm whether the tour captain, Sam Warburton, will definitely start at openside flanker when the three-match series kicks off in Brisbane.

North and Tuilagi, along with Brian O'Driscoll, will miss Saturday's game against the NSW Waratahs and the management fear the two young powerhouses will struggle to face the Wallabies at Suncorp Stadium on Saturday week.

North has a tweaked hamstring and Tuilagi has an injured shoulder. "There are one or two who are a bit sore and may be out of contention next week because they won't have been fit enough early enough in the week," admitted Gatland. "By the time next Saturday comes around one or two are possibly going to be ruled out."

The 34-year-old O'Driscoll, the Lions captain in 2005, is being deliberately rested with the Tests in mind but Gatland once again stopped short of guaranteeing his chosen 2013 leader a starting role. As the 24-year-old Warburton has had just 74 minutes of competitive rugby on tour and faces rivals for his position, a convincing performance this weekend would be timely.

"There is competition there and it'll be a long night when we pick the Test back row," stressed Gatland. "I have been 100% consistent from day one … it's about picking the best players and I haven't changed that tune. Sam's well aware of that. He had a good blow-out last week against the Reds with a couple of good turnovers so we'll see what happens on Saturday. Let's let the game unfold, rather than trying to predict and create some controversy about potentially leaving one of two players out of the team."

Gatland, for now, is ruling out any prospect of Warburton playing at No6 with Justin Tipuric at No7, the combination which served Wales so well against England in the Six Nations. "We don't have injury concerns among the back-row guys so we don't need to go down that road yet," said Gatland, who has picked England's Tom Croft on the blindside for the Waratahs fixture and named the Irish duo of Simon Zebo and Rob Kearney in his 23-man squad. Mako Vunipola has a chance to nail down the loosehead prop position, although Gatland says he has yet to finalise his preferred Test XV. "We said to the players that there's an opportunity for them on Saturday to stake claims but the Test team won't be selected until after Tuesday's game."

With four replacements having already been summoned to Australia, however, the management are likely to recommend larger squads for future Lions tours. "Even from four years ago there's been a step up in physicality and handling two games a week is tough," Gatland said. "It's something we need to be mindful of, particularly at the end of the tour if you're writing a report. Do you need a bigger squad because of that step up in physicality?"

The Lions have also opted to rest O'Driscoll to ensure his readiness for the Test series, which Gatland fully expects to be a shuddering collision. "We've spoken to Brian and Paul O'Connell … it's about being smart how we manage them. We want to make sure they are fit for when next required."

The Australian Rugby Union, meanwhile, are to distribute 50,000 golden "Lion-hunting" pith helmets to supporters to try to dilute the sea of red Lions replica jerseys anticipated at the Test stadiums.

Lions (v NSW Waratahs): Halfpenny; Maitland, Davies, Roberts, Zebo; Sexton, Phillips; Vunipola, T Youngs, A Jones; AW Jones, O'Connell; Croft, Warburton (capt), Heaslip. Replacements: Hibbard, Corbisiero, Cole, Parling, Lydiate, B Youngs, Farrell, Kearney