Lydiate facing Boks despite operation
Lydiate, who suffered the injury in a pool match against Fiji has had an operation on his eye so that he can start at blindside flank.
The 27-year-old missed last week's 6-15 defeat by Australia in the Pool A decider – a match in which he could have played according to Wales coach Warren Gatland.
Instead, Wales opted to bring in breakdown specialist Justin Tipuric to face the Wallabies.
But now Gatland has decided Lydiate's renowned tackling skills are required against the ever physical Springboks.
"It was a really tough game last week and we compromised ourselves a bit with Sam at six and Justin at seven," said Gatland at Wales' training base in Weybridge, southwest of London, on Thursday.
"We hadn't considered Dan at all with the knock he'd taken to the eye. We felt that with South Africa going back to a tried and tested physical approach, we needed to match that physicality which is why we've gone back to that balance with a genuine seven on the ball.
"Dan won't need any extra protection. The plate was inserted into his eye socket.
"He was fit for last week, but we made decision that we didn't select him. He's fine."
Gatland, who guided Wales to a World Cup semi-final in his native New Zealand four years ago, said: "After coming through an incredibly tough Pool, we are excited to be in the quarter-finals and returning to Twickenham."
Two-time world champions South Africa started the World Cup with a shock 34-32 loss to Japan but then won their next three matches to top Pool B
"They have grown game-on-game in this tournament and we know the challenge that faces us from a talented South African side," Gatland added.
Wales lost 16 matches in a row to the Springboks before winning their most recent encounter 12-6 in Cardiff in November.
Their only previous World Cup match saw South Africa emerge 17-16 winners in a tense pool clash in Wellington four years ago.
Agence France-Presse
