Ireland lock O'Connell, who is on his third Lions tour, is widely expected to forge the Test second-row partnership alongside Welshman Alun-Wyn Jones. But the 33-year-old is taking nothing for granted ahead of what should be his seventh Test match appearance in Lions colours.
"There is savage competition for places, and guys are very eager to play as well as they can individually," said O'Connell, who was part of the 2005 squad whitewashed by New Zealand and then captained the Lions in South Africa four years ago.
"I think if you look at the back-line and the way the backs have been playing it's certainly a step up. Forwards-wise, I think we've performed really well as well. We've carried well, done well at the breakdown at times and it's as good as any team I've been on, but you don't really know until you get to the Tests."
The Lions will chase a sixth successive tour win against the Brumbies on Tuesday, having so far amassed 261 points and 33 tries Down Under. It is form that has seen them installed as Test series favourites by many pundits.
But O'Connell knows Australia will be fierce opponents, adding: "We've a very tough three weeks ahead of us. Australia are a really good side, they have a lot of incredibly talented players and the next three weeks will be really tough and will be a lot different to what we've experienced (so far) in terms of intensity and physicality. It will be a big step up for us."
Meanwhile, Lions team doctor James Robson has delivered contrasting medical updates on Wales backs Jamie Roberts and George North ahead of next Saturday's first Test match appointment with Australia in Brisbane.
Centre Roberts limped off during Saturday's 47-17 victory against the New South Wales Waratahs, suffering a hamstring strain.
"Jamie is a grave doubt for this weekend, there is no doubt about that," Robson said. "You only had to see how much discomfort he was in at the weekend. However, further assessment will be made later in the week as to his availability going forward."
Wing North, though, is well on the way back following a hamstring problem. Robson added: "He (North) is an exceptional character and has worked really hard. He is back to running today. An accurate assessment on his availability for selection will take place on Wednesday. At the moment, I think he is doing very well and has a great chance of being fit for this week."
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