The Brumbies picked Lealiifano on the bench for the clash against the Queensland Reds on Friday night, but the 29-year-old felt his hamstring strain just 40 minutes before the team was announced.

The Brumbies scrambled to send Lealiifano for scans and had planned a fitness test in Brisbane on Thursday, but coach Stephen Larkham declared "it wasn't worth the risk".

It was a rollercoaster twist in Lealiifano's journey back to Super Rugby after he was diagnosed with leukaemia in August last year.

The injury hiccup happened so late Lealiifano will still have family at friends at Suncorp Stadium because it was too late to change their travel plans.

There are just two games left in the regular season and it's unlikely the Brumbies will risk Lealiifano on a trip to Hamilton next week to play the Waikato Chiefs.

But Larkham says the door is open for Lealiifano to play in a home quarter final on July 21 even if he's unable to play against the Chiefs or in Canberra club rugby.

"We'll see how he pulls up. If he doesn't loosen up, then maybe [he won't play against the Chiefs]," Larkham said.

"He felt his hamstring tighten up. It's just not worth risking at this stage.

"We'll make a decision [on Lealiifano playing], down the track. But if his body is right and his mind is right, he'll be available for selection."

Lealiifano's withdrawal was a tough pill to swallow after Lealiifano worked his way back into Super Rugby contention just 11 months after being diagnosed with cancer.

He has already ticked off significant milestones since being diagnosed and having a bone-marrow transplant with sister Sally, including returning to training and playing with his brother Lix in a Canberra fourth-grade game last week.

But instead of playing against the Reds, Lealiifano will be delivering messages as a waterboy as he edges closer to his Super Rugby moment.

So while it was devastating to have Lealiifano ruled in and then ruled out in almost the same breath, prop Ben Alexander, who will become the most capped player in Brumbies history on Friday night, said Lealiifano's cancer battle gave everyone perspective on the "minor obstacle".

"It's a little bit disappointing but you've just got to look at the bigger picture," Alexander said.

"[Lealiifano] is healthy, in remission and [a hamstring injury] is all irrelevant really. He's fit and healthy, that's all that matters.

"It will be awesome when he gets back on the field. But you've just got to look at the bigger picture of what he's facing and this is just a very minor obstacle for what he's faced.

"...When you get older you know what you're capable of. Christian will be confident and when he gets back on the field he'll be able to perform. We're confident he'll be able to do it."

Alexander will pass George Smith's record of 142 games for the Brumbies when he gets on the field against the Reds.

The Brumbies have named a powerful bench despite the absence of Lealiifano, with Alexander to join scrumhalf Tomas Cubelli as reserve weapons.

Nigel Ah Wong joined the touring squad to replace Lealiifano as the Brumbies chase their fourth consecutive win.

Cubelli hasn't played a game this year after injuring his knee in a pre-season fixture, but the Argentina international said Lealiifano's courage helped motivate his recovery to play against the Reds.

"I used him as an inspiration during the injury, it made me feel like my injury was an easy thing to go [through]," Cubelli said.

"I think [Lealiifano] went through more difficult things so he will sort out [this hamstring injury] but the team will have him when we need him."

SUPER RUGBY ROUND 16

Friday: Queensland Reds v ACT Brumbies at Suncorp Stadium, 7.45pm. TV time: Live on Fox Sports 1.

Brumbies team: 15. Tom Banks, 14. Henry Speight, 13. Tevita Kuridrani, 12. Kyle Godwin, 11. Aidan Toua, 10. Wharenui Hawera, 9. Joe Powell, 8. Jordan Smiler, 7. Chris Alcock, 6. Scott Fardy, 5. Sam Carter, 4. Rory Arnold, 3. Allan Alaalatoa, 2. Josh Mann-Rea, 1. Scott Sio. Reserves: 16. Robbie Abel, 17. Ben Alexander, 18. Les Leuluaialii-Makin, 19. Blake Enever, 20. Jarrad Butler, 21. Tomas Cubelli, 22. Nigel Ah Wong, 23. Andrew Smith.

Reds team: 15. Karmichael Hunt, 14. Izaia Perese, 13. Campbell Magnay, 12. Duncan Paia'aua, 11. Eto Nabuli, 10. Quade Cooper, 9. James Tuttle, 8. Adam Korczyk, 7. George Smith, 6. Rob Simmons, 5. Izack Rodda, 4. Kane Douglas, 3. Taniela Tupou, 2. Stephen Moore, 1. Sef Faagase. Reserves: 16. Alex Mafi, 17. Markus Vanzati , 18. Sam Talakai, 19. Cadeyrn Neville, 20. Caleb Timu, 21. Moses Sorovi, 22. Hamish Stewart, 23. Chris Kuridrani.