In the video shared by the Abu Dhabi Police, speeding cars are seen crashing into vehicles as traffic builds up unexpectedly
Williams, who has won 62 caps and started all of Wales's World Cup games except one, is not expected to recover in time for their next match - either the final or third-place playoff.
Leigh Halfpenny is expected to replace the 28-year-old in the lineup against South Africa when Warren Gatland announces the team on Friday.
Wales are already without loose forward Josh Navidi, who injured his hamstring in their 20-19 quarterfinal victory over France on Sunday, with winger Owen Lane called up as a replacement.
The Six Nations champions are also keeping a close watch on centre Jonathan Davies, who was ruled out of the quarter-final clash with a recurrence of a knee injury which he had aggravated in the penultimate pool game against Fiji.
South Africa also suffered a big blow ahead of the semifinal when winger Cheslin Kolbe was ruled out of the game with injury.
The winner of Sunday's semifinal will meet either England or New Zealand in the Nov. 2 World Cup final.
In the video shared by the Abu Dhabi Police, speeding cars are seen crashing into vehicles as traffic builds up unexpectedly
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