Liam Williams will miss the rest of Wales' World Cup campaign after suffering an ankle injury in training.
The Welsh Rugby Union confirmed his absence from Sunday's semi-final against South Africa, and then either the final or third and fourth place play-off next week.
"Liam Williams has been ruled out for the remainder of the Rugby World Cup following an ankle injury sustained in an accidental collision during training. His prognosis will be established in the forthcoming days," the WRU said in a statement.
The WRU added no replacement for Williams had been called up at this stage.
Leigh Halfpenny will feature at full-back instead of Williams against the Springboks, and centre Jonathan Davies has been named in the team after recovering from a knee injury that sidelined him for last weekend's quarter-final victory over France.
Davies replaces Owen Watkin, lining up alongside Hadleigh Parkes in midfield, while in a third change, number eight Ross Moriarty takes over from Josh Navidi.
Navidi suffered a hamstring injury in the France game, and had already been ruled out of the rest of the tournament.
The loss of 62 times-capped Saracens star Williams – arguably the northern hemisphere's finest attacking full-back – is a huge blow for Wales head coach Warren Gatland.
The 28-year-old British and Irish Lions Test player was in contention for a remarkable individual grand slam this year.
Aside from chasing World Cup glory, he helped Wales land the Six Nations title in March, then shone when Saracens won the Heineken Champions Cup and Gallagher Premiership.
The experienced Halfpenny has made one start in the tournament – against final pool stage opponents Uruguay – and went on as a replacement against Georgia.
Meanwhile, scrum-half Gareth Davies will win his 50th cap, partnering Dan Biggar at half-back in Yokohama.
Gatland retains the same front-five that has served him well during the tournament, with skipper Alun Wyn Jones making his 142nd Test appearance for Wales and the Lions.
That puts him level with Itay captain Sergio Parisse on international rugby's all-time appearance chart, just six Tests behind New Zealand World Cup-winning skipper Richie McCaw.
