Leigh Halfpenny has been ruled out of Wales' clash against South Africa on Saturday.
The Scarlets full-back has not recovered after suffering concussion following a challenge by Australia centre Samu Kerevi in Wales' 9-6 win over the Wallabies earlier this month.
Wales assistant coach Rob Howley said: "Leigh is out. He did some training on Saturday morning and was feeling a little bit light headed. Only common sense."
Howley also added that George North had returned to full training and is available for the match against the Springboks.
Wales will make it nine wins in a row if they win in Cardiff on Saturday.
"South Africa will be highly motivated. There's a landscape when we play South Africa. The contact area is pretty crucial," said Howley.
"When we play South Africa, there always seems to be a lot of aerial kicking. We always enjoy playing South Africa.
"It will be one of our toughest games this autumn but we have certainly got a lot of self-belief and confidence. The players don't want that streak to end."
A win at South Africa's expense would give Wales a first four-Test autumn clean sweep, while they are also chasing a ninth successive victory against all opponents for the first time since 1999.
When Wales last posted a ninth victory on the bounce - in the 1999 World Cup opener against Argentina - Howley was scrum-half and captain.
"It is a different era when you look back and compare and contrast," Howley said. "You make your own history when you wear the national jersey. Let's get Saturday over, and hopefully it will be a winning game.
"Personally, I have never experienced a squad with the strength in depth that we have got, with everyone that is given an opportunity taking that opportunity.
"International rugby is about winning also, and it's not always about style, it's substance also. There has been really good substance in our games over the last few weeks."