With Wallabies front rower Tom Robertson still on the comeback trail from a knee reconstruction, 22-year-old Johnson-Holmes has started each of the Waratahs first eight games.

He's already logged around twice as many minutes as he did last year, when all of his appearances in his first season were off the bench and could well push for Wallabies selection this year.

The Tahs prop had brief stints against South African teams in 2018, but Johnson-Holmes is likely to start, some, if not all, of the Tahs next three games against sides from that country.

He could well come up against the Sharks' Springboks prop Coenrad Oosthuizen at Sydney's Bankwest Stadium on Saturday.

His forward colleagues have no doubt the youngster will cope with whatever is thrown his way.

"It will be a challenge for him, but as he's done all year he'll front up and and take it on," Waratahs; lock Tom Staniforth said.

"He's competitive, he's definitely got the scrumming ability.

"I'm really excited to watch him play and he's doing really well."

Staniforth recognised that all the Tahs forwards would be tested on the weekend and would need to match the physicality of what he described as a typical South African pack.

"Big, strong, physical but we've just got to front up there's no two ways about it," Staniforth said.

"They are going to try and run over us and we're going to do our best to stop them.

"If you underestimate them they will burn you."

Australian Associated Press