It will be only the Wales flanker's second start on tour, with some pundits suggesting he could be under pressure for a place in next week's first Test starting line-up. But the back-row on Saturday of Tom Croft, Warburton and Jamie Heaslip could also be the one Lions head coach Warren Gatland decides to go with against Australia in Brisbane.
"I have been very impressed with Sam," Lions assistant coach and forwards guru Graham Rowntree said. "He is very professional. He is certainly not showing any signs of stress or pressure. Like all the other players, he goes about his business. I have been really impressed with him as a person."
He addedL "He is a doer, and a lot of guys are following his lead in terms of his attitude to training, his diligence.
"It is not getting any easier in terms of selection. There are a lot of guys putting their hands up. We will get tomorrow (Saturday) out of the way, and then Tuesday (against the Brumbies), and then we will pick a Test team. That is the truth."
Rowntree added that it is hoped Scotland lock Richie Gray will be fit for the Brumbies clash, while wing George North (tight hamstring) took no part in Friday's work-out, although centre Manu Tuilagi did as he continues his recovery from a shoulder injury.
"He (Gray) has got a bump on his shoulder," Rowntree said. "He is certainly not fit for this weekend, and we are hoping he is going to be fit for Tuesday. At this stage, I am counting on him being fit for Tuesday."
The Lions lineout had its moments of malfunction during last Tuesday's 64-0 stroll over a Combined Country XV in Newcastle, while the Waratahs are boosted by key forward Dave Dennis being temporarily released from pre-Test series Wallabies training.
"Dave Dennis coming back in will bolster their lineout for tomorrow. He's a good player, he has got some Test experience," Rowntree said. "We had a few issues in the lineout on Tuesday night. We dropped three from 16, but a lot of that was just personnel that hadn't played a lot together.
"That's what you get on a tour like this. You take it on the chin and move on. I actually thought they battled very well as a pack on Tuesday night. They didn't really get enough credit for the performance they put in."
- Sports & Recreation
- Graham Rowntree
- Warren Gatland
- Jamie Heaslip