Head doctor James Robson confirmed that he is ready to give Wales back row man Warburton the all clear to rejoin team training ahead of Wednesday night's opening game in Perth against the Western Force, subject to a final fitness check on Sunday.
"Sam got a knock in training last week that seemed fairly innocuous. But then he just felt his knee stiffen up a little on the flight and we pulled him out of training," said Dr Robson.
"We felt it would be beneficial to put a bit of steroid into the knee to help with the discomfort and Sam has had enormous benefit from that. It is only a mild tweak of a few fibres of his ligament and the muscle.
"Given that he didn't play against the Barbarians he should be available for the next game. He has had a five day graduated return to playing - you inject, you rest and then you give a graduated return and he has been doing some rehabilitation training with us and medically should be fit to return."
Whether or not the management throw Warburton into the game in Perth, or rest him for Saturday's game against Queensland Reds on Saturday in Brisbane remains to be seen, but a fit again O'Brien, who has been suffering from deep bone bruising in a leg injury that kept him out of Leinster's RaboDirect PRO12 final triumph over Ulster, is a candidate for the No 7 jersey on Wednesday night.
The only other injury concern surrounds Irish full back Rob Kearney who, like O'Brien, missed the final against Ulster after pulling up in the warm-up with a stiff hamstring. The good news on him is that he is up and running and poised to be released back to team training.
"Rob is doing well and is running today. He had a niggle, allegedly, in his hamstring, but it might have been referred pain in his back," said Dr Robson.
"He is moving nicely again now. We are being cautious with him and we hope we can release him back to team duties on Monday."
Now on his sixth Lions tour, Dr Robson was delighted at the outcome of the first game on the injury front, with only two players requiring stitches - skipper Paul O'Connell and replacement hooker Tom Youngs.
"They were tough conditions out there and I am delighted we have less damage than I would normally expect in a normal Test match. Two guys required stitches, but those were accidents," said Dr Robson.
"I am expecting all the boys to wake up feeling fairly good about themselves this morning. On average they lost about 2 kilos during the game last night - they were weighed out and weighed in and they filled with fluids very well during the game."