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Wales boss Warren Gatland says there are "probably 25 or 26 players" nailed on for his World Cup squad going into Saturday's warm-up clash against Ireland at the Aviva Stadium.

Gatland will field several of his big-guns for the Ireland return fixture, which comes three weeks after the reigning RBS 6 Nations champions claimed a 35-21 victory in Cardiff.

Skipper Sam Warburton is a notable absentee, although Gatland described his shoulder knock as "nothing serious," with lock Alun-Wyn Jones leading a team that includes the likes of George North, Jamie Roberts, Dan Biggar, Rhys Webb and Taulupe Faletau.

North reaches the 50-cap landmark in what will be his first appearance for five months after suffering three concussions last season, and there is a Test debut for York-born Exeter prop Tomas Francis, whose grandmother Eirlys is from the Swansea Valley.

Gatland will announce his 31-man World Cup squad in Cardiff next Monday, and he said: "To be honest, there are probably 25 or 26 players that are nailed on, and then there is the rest of the squad - it's either/or and making the decision and just trying to get the balance right.

"We haven't finalised whether it's going to be an 18-13 or a 17-14 split (between backs and forwards). We are probably leaning towards the 17-14 split at the moment, but things change.

"We will see how the weekend goes and how the performances go, and hopefully we won't pick up too many injuries.

"Given the history of World Cups, the players who do miss out are going to be incredibly unlucky, but they are going to be pretty valuable to us as well if there a couple of knocks and we need to call people in. They have just got to keep themselves in pretty good shape.

"When you are picking a World Cup squad, you have got to take your chances. You have seen players in the past that have taken their chances and been selected, and there are others for whatever reason it didn't go their way and they missed out.

"That is the reality of having to pick a squad and make hard decisions, particularly in 50-50 calls. So for a few players on Saturday, whether they are in the starting XV or the bench, their impact or their performances are pretty important."

North has not played since being knocked unconscious during his club Northampton's Aviva Premiership victory over Wasps on March 27.

But he has passed all the required tests and successfully came through a Wales squad training match in north Wales earlier this month, while Wales staged another practice game this week against the Ospreys.

Gatland added: "We've had two pretty full-on hit-ups. I have no doubt he will be up to speed, and with the rest and the protocols we have done, the concussion issues he had shouldn't be a problem."

And reflecting on 23-year-old Francis' rapid rise through the ranks, Gatland said: "We have been really impressed with the way Tom has developed since he was with us in the Six Nations.

"The way he has trained, his conditioning and the amount of weight he's lost as well - he's in good shape.

"He has lost about seven or eight kgs. Conditioning-wise, he has just continued to improve. He is probably in the best shape of his life.

"I don't expect tight forwards sometimes to be at their best until they are 27 and 28, so he has got a lot of time to improve, and for us it's just about him enjoying the opportunity on Saturday and just doing the basics well. If he does that, then we will be more than happy."