Ospreys midfield star Hook will delay shoulder surgery by another week as Wales target only a second win in 104 years of fixtures against the reigning world champions.
But while Hook prepares for his final game probably until late September, Wales have lost the services of their record try-scorer Shane Williams.
Hook's Ospreys colleague also has shoulder trouble and he will miss the Springboks clash, together with Wales' Tests against New Zealand in Dunedin and Hamilton later this month.
Uncapped Newport Gwent Dragons prospect Will Harries takes Williams' place on tour, with the diminutive wing joining Hook, Martyn Williams, Dwayne Peel, Gethin Jenkins and Luke Charteris in sitting out the summer trip.
Hook's appearance on Saturday comes after he had originally been sidelined for the game, but he now continues his prolific centre partnership alongside Jamie Roberts.
"To be honest, I didn't need much persuading," said the 24-year-old, who wins his 43rd cap.
"I had gone this far through the season, and I have made myself available for what will be a great game.
"Obviously, it is a problem that needs to be sorted, but an extra week shouldn't make any difference at all, really.
"Once the surgeon goes in and does what he has to do, he will decide how long it will be. Hopefully, it will be between three and four months and I can be back around September.
"I am having pain-killing injections, and that is helping me along. I can't really do much more damage to it, it's just the pain factor and getting through that.
"For the last five months, I have been managing it and doing what is best for myself."
Wales head coach Warren Gatland added: "I think it is fantastic for James to be available, and the support from the Ospreys has been great.
"He will play this Saturday, and then get the operation done next week. It has worked out fantastically to have someone of his creative ability available - it's great news for Wales.
"You only have to look at the man-of-the-match awards and player-of-the-year awards James has been picking up to see what a great asset he is to any team.
"We will be facing the world champions a stronger team because of his involvement."
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