The fixture falls outside of the international window, so Wales will be without 13 of their players, South Africa likely a similar number too.
The Springboks will be heavy favourites, but Grobbelaar says they are taking nothing for granted.
“There have been a few good games over the last few weeks and actually some big away games that we’ve won,” Grobbelaar said.
“The team’s done really well (in November) and now it’s the last one for us against Wales. I don’t think there’ll be any lack of motivation from the guys, I think we’ll handle it with the same intensity as other Test weeks.
“Maybe there’ll be some new combinations, some new guys getting opportunities but I think everyone’s going to be 100% in.”
Grobbelaar maintains Wales are a good team despite their recent troubles.
“They have some great rugby players. As we saw (against New Zealand on Saturday) they can score some beautiful tries, they’ve got a good skill set at the back and they’re always a threat under the high ball.
“Over the last few years, we’ve gotten to know some of the Welsh players through the URC, so there’ll be some familiar faces. On paper, we’re maybe the favourites, but knowing the Welsh after playing them in the URC, they’re a proud nation that won’t go away and it’ll be a full-on battle for 80 minutes.”
Despite missing players, Grobbelaar says the large Springbok squad that has been on tour will help them with combinations and continuity.
“I think what has helped us is training together these last few weeks,” he said. “We’ve been mixing players, so we really got to know each other, even the younger guys who I haven’t played with a lot.
“So this weekend – with some new combinations – I’m sure we’ll be ready for the battle.”