Graham Rowntree has revealed the intense attention to detail that is underpinning the British and Irish Lions' team selection for next week's Test series opener against Australia in Brisbane.

The Lions play their penultimate warm-up game today, ahead of next Thursday's team announcement, facing New South Wales Waratahs at the Allianz Stadium in Sydney. Asked if the selection process had been ongoing since the tour opener against the Barbarians in Hong Kong two weeks ago, Rowntree, the Lions assistant coach said: "We have been doing that since the very first training session at our Vale of Glamorgan base [last month].

"We watch how the guys are in the environment, who the diligent ones are, watching the computer, who are the ones learning the calls. We watch training videos back, see how the body language is. We are watching them 24/7. I must say I have been very impressed. They are everything I expected. They have all been very professional."

The possible Lions Test pack – Mako Vunipola, Tom Youngs, Adam Jones, Alun-Wyn Jones, Paul O'Connell, Tom Croft, Sam Warburton and Jamie Heaslip – will be in action tomorrow, along with probable Test half-backs Jonathan Sexton and Mike Phillips. Sean Maitland is the only Scotland player to feature.

But the coaching staff have maintained throughout that they will not begin making definitive Test team decisions until after Tuesday's match against the Brumbies in Canberra.

"It will be tough [today], this fixture 12 years ago was fairly tough," Rowntree added. Guys have really got to take their opportunities because we are watching, in training as well. We got a good test last week [against Queensland Reds. Crikey, they ran us ragged. I am sure the Waratahs will give us another work-out. It wasn't an 80-minute performance last Saturday and we have certainly looked at that in review. The third quarter was littered with errors which really broke our stride."

Among those hoping for an opportunity tomorrow will be the Ireland full-back Rob Kearney. He has recovered from a torn hamstring and takes a seat on the replacements' bench. "I spoke to Gats [Warren Gatland, the Lions head coach] in Hong Kong and he said if you need two weeks, take it," Kearney said. "When you have that sort of clarity there from a coach it makes it pretty easy to focus your own mind. You don't start wandering too much.

"I took a huge amount of solace from that and it spurred me on to get fit that little bit quicker to repay that faith he showed in me. I think this is a much stronger squad than four years ago [in South Africa]. It is younger, but it still has that experience as well.

"What is great about this squad is there are so many Test players in it. You could happily see anyone on the field playing against the Aussies and doing a pretty good job, whereas four years ago in South Africa we might not have had the same depth."

The Waratahs are without several players who are away with the Wallabies for pre-Test series training, but Dave Dennis, the captain, and the centre Rob Horne have been released back to play.

For both, today's game will provide a first-hand insight into what Australia can expect next week. "We can't predict what they are going to throw at us in the first Test," Dennis said. "But playing tomorrow will give us a better idea of what we are going to face. There is a chance I may not be selected in the Test series, so this could be my first and last opportunity to play them, or it could be the first of four.

"We are just going to keep it simple, be physical and go at them. We're not going to get bogged down in the fact they are the Lions and we are the poor old Waratahs. The reality is it's a two-horse race and we are going to try to knock them off.

"We need to hold on to the ball and play how we've played all year. But we need to do that at another level, a higher intensity. They don't know what they are going to face until we get out there. Likewise, we don't know what they're going to throw at us."

TEAMS

New South Wales Waratahs v British & Irish Lions, Allianz Stadium, Sydney, today, 10.30 BST

Waratahs D Mitchell; C Crawford, R Horne, T Carter, P Betham; B Foley, B McKibbin; J Tilse, J Ulugia, P Ryan, W Skelton, O Atkins, J Holloway, P McCutcheon, D Dennis (capt)

Substitutes: L Holmes, R Aho, S Talakai, L Timani, A J Gilbert, M Lucas, B Volavola, T Kingston.

Lions L Halfpenny (Wales); S Maitland (Scotland), J Davies (Wales), J Roberts (Wales), S Zebo (Ireland); J Sexton (Ireland), M Phillips (Wales); M Vunipola (England), T Youngs (England), A Jones (Wales), A-W Jones (Wales), P O'Connell (Ireland), T Croft (England), S Warburton (Wales, capt), J Heaslip (Ireland).

Substitutes: R Hibbard (Wales), A Corbisiero (England), D Cole (England), G Parling (England), D Lydiate (Wales), B Youngs (England), O Farrell (England), R Kearney (Ireland)

Referee Jaco Peyper (South Africa).

Assistant referees Jerome Garces (France), Glen Jackson (New Zealand)