Wales head coach Warren Gatland says Alex Cuthbert and Johnny Williams know they must perform strongly against South Africa if they are to be in with a chance of heading to the Rugby World Cup . Both players will make their first appearances of the summer warm-up schedule at the Principality Stadium on Saturday, although the head coach says he is not expecting complete 80-minute performances from the duo. Dan Biggar and Liam Williams have been withdrawn as injury precautions. The WRU say Biggar has a back irritation and Williams has a tight hamstring. Sam Costelow will instead start at fly-half and Cai Evans will make his debut at full-back on Saturday, with Tom Rogers coming onto the bench. Here's everything the Wales boss had to say at a press conference on Thursday: Question: Can you talk us through the injuries and changes to the matchday squad? Warren Gatland: "Not serious at all. Both of them [Williams and Biggar], if we pushed them hard, could play on Saturday, but the decision was made there is no point taking a risk at this stage. "I see it as a positive, really. It's dealing with things that are going to been thrown at you. It's using a bit of adversity as a positive." What's your reaction to the Owen Farrell story, with World Rugby appealing the overturning of his red card? "I have got no comment on the Owen Farrell thing. That's last week, and we are just focusing on South Africa. We are focusing on ourselves and not the past." You've made a lot of changes to this Wales team for South Africa - can you talk us through them? "There was always going to be some changes. We have been so impressed with this group of players, and as it has turned out there was an opportunity for us to give everyone a chance to put their hand up. We feel that the time we've had together, we've increased the depth and competition within the squad. "A number of teams have picked up one or two injuries, so you have got to have players who have been with you for that period, hopefully had some game-time and been training with the squad." Does Jac Morgan being named captain for this game mean he will be World Cup captain? "He did a great job in the first game, and he gets another chance to lead the team out on Saturday." Are you close to knowing your final World Cup squad? "I think we are getting a little bit closer. There is an opportunity for players on Saturday. We will come back as a coaching group after the game and finalise the squad. We are confident that those players carrying injuries are going to be available for the first game against Fiji. "We had Bradley Roberts in today. We called him in as cover for the weekend, potentially. If this was a World Cup semi-final, Dan Biggar would have been fine for the weekend. We are just taking a precautionary measure. There is no need for us to take a risk with him." Nigel Walker made a ringing endorsement of you today, backing you to remain as Wales head coach through to the 2027 World Cup given you are one of the best coaches in the world. W hat do you make of that? "We'll see how the World Cup goes! I am just focusing on the short term. I have never been a person who thinks long term too much in terms of my own personal situation. I am a great believer in what will be will be. I have already said that the work this group have done and strides we have made, I think we can do something pretty special at this World Cup, and I honestly believe that. If that happens, then those other things take care of themselves." How are Dewi Lake and Taine Plumtree? "Dewi is talking to the medics today. He has a little bit of a knee issue, and they are confident if he carries on with his rehab he will be fit for the first game, and the same prognosis for Taine." Are Johnny williams and Alex Cuthbert playing for World Cup places or will their experience count? "I've had a chat with both of them. They’re well aware of the situation they're in. I'm not looking for an 80-minute performance because they haven't had a lot of rugby but I think they’re pretty well aware they've got to go out and give a really strong performance to be able to put their hand up, considering the work the other players have done and how long that they've been in the squad. They've been unlucky but they both get an opportunity on Saturday." What does Saturday night, Sunday and Monday look like? "Saturday night is just finalising the squad. We’ll get a pretty detailed injury update in terms of all the players in the squad, the ones carrying knocks and when they can return to full-time training, when they're available. "Sunday will be a rehash of that and potentially there may be one or two decisions which has happened in the past where we’re still undecided and we might sleep on it and make a final decision potentially on the Sunday. "Then it's a matter of notifying the players and announcing the squad on Monday. It will be individually [telling the players]." How many injured players can you carry in the squad? "Maybe one or two. That's probably the number you talk about. "I think the important thing is when you can get back to training. "If you look at the draw, you've obviously got to go fully loaded for the first game, then looking at Portugal with a six-day turnaround there'll be changes, then you've got eight days to Australia where you'll be a strong side again and then a 13-day turnaround where hopefully everyone gets an opportunity to recover from any bangs and bruises before you play Georgia. "I think there's less pressure in this tournament than there has been in the past where you've had four-day turnarounds when that's had quite a significant impact on the squad. "That's a discussion we'll have in terms of risk and how many we can carry. "We have in the past gone to World Cups carrying players with niggles that are going to take two or three weeks to come right. That may be the case but it's just depending on what sort of risk do you potentially take." How is Taine Basham? "He’s had a full week with us from Monday, he passed his HIA 2 and 3. No problem at all. He felt fine after the game. He felt fine when he was on the field. It was an independent doctor who had a look and said they wanted him to have a HIA." Are you concerned that clarity isn’t there regarding cards? "For all of us, what we want is certainty and clarity. That's what you're hoping for from the referees, not just the officials, not just those sorts of situations but any situations." Do you feel you're able to tell players at the moment ‘this is the correct technique - you won't be penalised if you do it this way'? "Yes." So why do you think Owen Farrell is in this situation he's in? "I've already said I don't want to talk about the Owen Farrell situation. That's already been spoken about. I don't want to talk about it." You were pretty forthright about it in your newspaper column... "I was forthright about the fact he's got to get his technique a little bit better. "It's something we talk with players about: if you don't bend at the hips then you're putting yourself in a situation that you can potentially get yellow carded or red carded. "I’d like to think all coaches talk about tackle technique and getting those things right. And if you don't get those things right, then you can potentially put yourselves in a position where you can be carded." Will new audiences be confused by this situation? "I'm not sure. I don't know the answer to that. I'm just waiting to see what the final outcome of that is. Everyone wants clarity and certainty about all aspects of the game."