I'm gutted that Lee Byrne's out of this tour, and it just shows how fickle playing for the Lions can be.
One minute you're one of the main players, the next you're on the plane home.
I only found out about the injury at the end of our training session on Thursday morning.
The forwards had been on a different pitch to Lee and the rest of the backs, practising scrummaging.
It was only when we came back to the changing room and saw him with the medics that we realised something was wrong.
Apparently he had injured his thumb in a completely innocuous incident while the backs were going through one of their moves.
I really feel for him. He's obviously a mate of mine from the Wales team and had taken his outstanding Six Nations form into this tour.
Jones, Rees and Jenkins are the first all-Welsh Lions front row since 1955
Unfortunately things just haven't gone for him since the Tests started. First he had to come off on Saturday because of his foot and now this has put him out for the last two games.
We're just fortunate to have someone as good as Rob Kearney to step in at full-back. He did really well when he came on on Saturday and I'm sure he'll perform again in Pretoria.
Talking about how fickle a tour can be, who would have predicted an all-Welsh front row for one of the Tests?
You would have got long odds for that at the start of the tour.
It's been a long, long time since that last happened and Adam Jones and Matthew Rees - who we all know as Smiler - deserve their opportunities after making a huge impact as replacements last weekend.
Before you ask, I don't know where the nickname Smiler comes from, but no-one in the Wales squad or here ever calls him Matthew.
He actually grew up not far from me, in Tonyrefail in the Rhondda, and starting won't phase him at all.
There's a really good feeling in the camp and we know that if we can just get that win on Saturday, it will be a fantastic last week
He's got plenty of experience and showed what he could do last weekend, when he was strong at the set piece and immense in the loose.
I'm really disappointed for Vicks and Mearsy, who have made way. I knew Vicks well from the 2001 tour but have only just got to know Lee and credit to him, he's been a huge part of this tour.
You couldn't wish to meet a nicer bloke and he's a fine player.
As for me, I'm obviously disappointed not to start, because that's what everyone wants to do.
To be in the 22 is still a big thing though and hopefully I'll be able to come off the bench and make a bit of an impact.
When you're on the bench you're in limbo a little bit, because you could be on after five minutes or not at all.
You just have to be patient and I'm willing to help the team in whatever way possible.
This week the forwards have spent a lot of time on scrummaging after the problems we had in that area last weekend.
We've also worked on the driving maul, because conceding a try from one last weekend was tough to take.
I don't think we need to drastically change the way we play on Saturday though, just cut out the errors and make a good start rather than giving them an early 13-point lead like we did last week.
The coaches have been emphasising that we need to be there or thereabouts after an hour, then we've got a great chance.
It's reality that some of the players in the squad will have already played their last match, but no-one will know that yet.
On the previous tours I've been on, people thought it was all over for them and suddenly there was an injury and they were in the Test side.
You never know on a Lions tour and it's crucial that players don't go "off tour".
I really don't think that will be a problem though. Everyone is still really hungry to be involved and our training sessions have been excellent.
I know it's a cliché, but the boys not in the 22 are as important as the ones who are.
There's a really good feeling in the camp and we know that if we can just get that win on Saturday, it will be a fantastic last week.
Martyn Williams was talking to BBC Sport's Simon Austin