Series depends on nursing Roberts back to health – Gatland's game plan simply cannot function if he's not on board
Welsh centre is the anchor this Lions side desperately needs to steady the ship and allow O'Driscoll to thrive
The Lions series could now hinge on the performance of a doctor and a medical team.
While everyone was wondering about the Wallabies and their injuries after the first Test, it is the tourists we have had to worry about after the second. Wounded by their one-point loss, a kick away from securing a historic win, the Lions need to put themselves back together both physically and mentally.
Warren Gatland and his coaches will know how to apply the psychological Band-aids, but for the physical issues it will be down to Dr James Robson, a six-tour veteran, and his crack medical team.
He saved my life on the 1997 tour to South Africa and I am not exaggerating when I say that the ability of his team to get one player back on his feet will probably decide the fate of this tour.
Adding to the pressure is the loss of Lions captain Sam Warburton to a torn hamstring. There is not much you can do about that, but I am hoping they have better luck with the same area on Jamie Roberts, the centre around whom Gatland would have been hoping to build his team and style of play.
A medical man himself, Roberts was injured a week before the first Test. He has been sorely missed, and the Lions' game plan, which revolves around the relatively simple idea of getting over the gain line up the middle, has been less effective without him.
His absence has meant that the team have struggled to find the rhythm and style they were looking to create.
In the early tour games, you saw someone who understood that he was there to do a job, who was focused, aware that Lions tours are remembered for nothing more than whether they are won or lost.
Roberts qualified as a doctor while playing professional rugby, which puts him in a different league to pretty much all others over the past 10 years.
Grand Slams, Six Nations championships, World Cups – he has delivered when it matters. He has been the linchpin for Wales, and that was the role the Lions needed him to fill this time around.
In attack, they need him running the classic inside centre line. All the other centres here are outside centres, including the bull-sized potential replacement Manu Tuilagi, who has had his own injury issues to deal with.
This means that they tend instinctively to run a line that attacks the outside shoulder of the men facing them. Those shoulders are further away from the breakdown, which makes it harder for the supporting players to arrive, and usually when tackles are made, they happen wider out.
It may seem a small thing, a matter of yards really, but it can derail a game plan such as Gatland's, which is based on creating pressure points in and around the fly-half channel, especially with ball off the top of a line-out.
What Roberts (right) does so well is come back against the grain and attack the inside shoulder of the opposing inside centre, more often than not involving the fly-half and openside flanker at the same time.
The point of contact is past the gain line, close in, and just where a player such as scrum-half Mike Phillips wants it. From here, the No 9 can either launch the backline, or snipe around the corner, either running himself or bringing bigger forwards on to the ball.
Without someone running the 'Roberts line', as I will call it, the Lions have been hit by a couple of problems. Their scrum-halves have been less effective and have been unable to bully the opposing back-row or bigger forwards making the breaks, as the Lions had hoped.
At the same time, the lack of Roberts has suddenly meant Brian O'Driscoll and Jonathan Davies becoming less effective. It is important to remember that the roles of inside centre and outside centre are very different, despite the fact that people often think they are interchangeable.
The skills needed can be picked up, but it takes time and often it is the small things that are the biggest issues.
If you want evidence of this, look at Roberts' other big strength, which is his role as defensive leader. He is used to bossing that channel because he does it regularly.
He understands the requirements of the inside centre when defending, and the subtle difference, an almost instinctive need to know when to charge up, hold or drift out.
As a No 12, you have to be the protector of the fly-half channel. Most teams attack it with predictable regularity, flooding it with runners. An inside centre has to be able to hold this area and push out and work with his outside centre to control and command the wider spaces.
Roberts can do this because he is big, and that counts when the opposition are trying to bring runners into the game. Davies is not small and he hits hard; however he simply lacks the presence of Roberts at No 12.
On top of this, the lack of a proper No 12 has had an impact on the two world-class No 13s. Davies has been forced to play out of position and O'Driscoll has missed a foil to play off.
The Irishman would be better alongside Roberts, as would Davies.
The last time the Lions won a series in 1997, they had Scott Gibbs and Jeremy Guscott as inside and outside centres. You could not get two more different players. This time round in Australia, the Welsh doctor could prove the perfect prescription for a win. (© Daily Telegraph, London)