Warming the bench isn't O'Brien's idea of a good time
Ireland's Simon Zebo, on Sunday, highlighted the need for players to take every opportunity afforded them to make an impression.
Zebo's natural exuberance and optimistic nature means he genuinely believes there is an opportunity for players to force their way into the Test 22.
He's not wrong although it would take quite a fairytale if Ulster duo Rory Best and Tom Court suddenly put themselves into the reckoning.
It is unlikely Zebo will force his way past George North, Tommy Bowe and Alex Cuthbert. He should have been on the bench ahead of Sean Maitland on Saturday but that wasn't the most frustrating of Warren Gatand's selection decisions on the night.
That honour was reserved for the decision to omit Sean O'Brien from the 23.
O'Brien was togged out and sat on the bench but as the 24th man just in case someone pulled up during the warm-up.
"It was frustrating," O'Brien chuckled yesterday. "I had to prepare like I was going to play just in case anything did happen. Doing the warm-up and feeling that buzz and then sitting on your chair for the rest of the match is disappointing obviously.
"But we all have a chance this weekend to stake a claim again and go out and show what we can do."
At this stage it is, of course, a fruitless exercise to speculate but just how effective would O'Brien have been with ball in hand during the final 20 minutes of that first Test?
Australia were already reeling from the physical battle that marked the occasion. At times the physicality was harsh and unrelenting and enough to make the eyes water. Australia's decimated backline and Paul O'Connell's fractured arm lend truth to that.
The sight of O'Brien running at their beleaguered defence with the ball tucked under his arm would have terrified the Australians.
It beggared belief that O'Brien's versatility and abilities did not merit the place on the bench that went to specialist blind-side flanker Dan Lydiate, who captains the side today in Geoff Parling's stead as the England international will replace Paul O'Connell in the Test team on Saturday.
Lydiate did see action in the first Test when he replaced Tom Croft but he was anonymous and must surely be under pressure to keep his place on the bench.
If O'Brien turns in yet another strong performance against the Rebels tonight surely he will be promoted to the replacements' bench at the very least for the second Test on Saturday.
"The coaches are telling us that we have a chance to break into the side and we have to put trust in them," said O'Brien.
"We can only look after ourselves. We have another match to play tomorrow and there is no point going out thinking we haven't a chance; that will only affect your performance.
"You have to do the best you can every opportunity you get in a Lions' jersey," he added.
O'Connell's absence will result in Sam Warburton continuing at open-side despite a less than stellar showing on Saturday.
O'Brien will not be alone in attempting to influence the selection for Saturday's second Test. His Ireland and Leinster team-mate Rob Kearney also has plenty to play for in this game.
That the full-back was not at his best in the loss to the Brumbies was understandable as it was his first start in a number of weeks.
If he shows a return to form today he will be a more palatable choice than Maitland for the bench.
This game has the potential to be an intriguing contest.
The Rebels are well down the pecking order in the Super 15 and are without their Wallabies Kurtley Beale, James O'Connor and Nick Phipps but coach Damien Hill has selected a competitive side.
"We've got a number of players on this team who are aspiring to be players for the Wallabies in the next couple of years and there's no better arena to be in to test those skills," said Hill.
"We want to test ourselves against the best and this is a great opportunity to do that. Just look at that back three, with Kearney and Zebo, it's a very good attacking back three, especially on the counter-attack; but that's the challenge as well."
Lions forwards' coach Graham Rowntree ensured that the tourists will certainly be competitive with his guarantee that "some of those playing on Tuesday will run out on Saturday" and he suggested that the Rebels will cause them problems.
"There are a lot of familiar names from the analysis we've done of their Super 15 outings," he added.
The Lions' last midweek game was a defeat against the Brumbies.
They bounced back to win Saturday's Test but with all that's happened in the meantime they desperately need to decent win tonight to build momentum for Saturday's second Test.