Jamie Roberts: That first surge of pain told me I was heading for Lions heartbreak

I definitely expect to be able to play a part later in the tour

The look on my face as I hobble off injured tells its own story (PA)

I knew from almost the very moment it happened, when I felt that first pain against the Waratahs last Saturday, that I would not be part of one of the greatest moments any rugby player could have: taking to the field in that famous red shirt in Brisbane today for the first match of the series. Part of me will be heartbroken sitting up in the stands this evening.

It has been a tough week personally. The timing could not have been worse – the week of a Lions Test and I tear my hamstring. I pretty much accepted in my head straight away that I would not make the Test and I guess that showed in how I looked as I came off the pitch and disappeared up the tunnel in Sydney last weekend. Gutting. But that’s the nature of the beast. You have to get over it. Injuries happen in rugby and if you can’t deal with it you are in the wrong sport.

I definitely expect to be able to play a part later in the tour. I would have been sent home by now if there was not the feeling within the medical staff that they can get me on to the pitch again.

You always aim for the next game. I am working really hard with the medics and physios and if I could put myself in contention for the second Test that would be fantastic. But it is a day at a time with these things. One day it feels great, another it doesn’t feel so good. It is pretty intensive treatment, a lot of icing, a lot of stretching, functional work with the physios. It is pretty much round-the-clock stuff. As anyone who has done a hamstring can tell you, it is a painstakingly slow process.

The danger is trying to push yourself too quickly because you are so desperate to get out there again. You can’t get ahead of yourself and you have to be brutally honest and admit when you are not 100 per cent fit. That is not always easy but you need to remind yourself that if you go out there without being 100 per cent you are not just letting yourself down, you are letting your team-mates down as well and I will not do that. I will not put myself forward for any matches on this tour unless I am ready.

I have been here before – most players have. I got knocked out against Argentina, one of a number of knocks I took last autumn, but then I kept being ready for the next game. The Wales boys gave me plenty of stick for that and started calling me Lazarus. There you go, I have been a quick healer in the past and here’s hoping I am again.

I know Jon will do me proud in my No 12 shirt

I’ve said before that I’m not a good watcher of any game and when one of this magnitude comes along it is massively disappointing not to have had the chance to be down there on the pitch. But like any of the injured players, I owe it to my team-mates not to mope around and when I look down on the guy who is wearing the No 12 shirt for the Lions it will give me a great deal of satisfaction.

I have tried to get involved when needed this week and pass on any advice I can. You have to back the boys who are being sent into the firing line today. There are times when you have to stay clear and give them space but in between there are moments to chat. I have had a good talk with Jonathan Davies, who usually plays alongside me at 13 for Wales but has moved inside for tonight’s game. I am so pleased for Jon winning his first Lions Test cap – it will be a special moment and, what is more, I am tipping him to be a man-of-the-match candidate.

He is an extremely good player and has shown on this tour that his all-round game has reached a fantastic level. He has never played better and has become absolute quality – and on top of all that he is a good mate. Hopefully, he can shine and the team can win. That’s what we are all here for, after all, and I do expect us to win today.

The first Test is crucial. In simple terms, win it and you are one win from the series, lose it and the pressure really is on for the second Test. In 2009 we lost the first one and then the second with a last-minute kick. That hurt and still does. So today is massive and the boys are revved up – it is the biggest game of their careers.

That defeat to South Africa four years ago – a series we could so easily have won – will be burning on the minds of the guys who were there: Brian O’Driscoll, Paul O’Connell, Mikey Phillips, Adam Jones, Tom Croft, Alun Wyn Jones. There is a lot of experience in this team, guys who have played in Lions Tests before and guys from 2009, and they will take that painful memory into tonight’s game.

Our defence must be on top form against Genia

The Australian line-up is interesting, with their three new caps. I expect them to challenge us with their kicking game. The teams we have played against so far have not really had an attacking kicking game but Australia will certainly look to get at us that way through the likes of Berrick Barnes and James O’Connor. Those two will test our back three.

But the boot is far from their only weapon. They have a running threat all over the pitch and we will have to be alert to the talents of Digby Ioane and Israel Folau on the wings. They are very dangerous runners so our defence needs to be top-drawer. But first and foremost we will have to deal with the threat posed by Will Genia, their No 9 and main man. He likes to attack defences, get across the pitch and make defenders take wrong decisions in and around the rucks. Dealing effectively with him is going to be a huge part of our defence.

Whatever the result in Brisbane tonight it doesn’t finish here. It is a long, tough process spread over three weeks and, hopefully, one that I can play a part in. I would not still be out here if there was not a chance of featuring again – there is no place for tourists out here.