'Naturally he's an athlete. Before he came in, he hadn't played rugby union before'

As if the beleaguered Sunwolves didn't have enough on their plate dealing with Super Rugby's new try-scoring king Israel Folau on Friday night.

Now it's potentially double trouble for the bottom-placed and soon-to-be-extinct Sunwolves, with Folau's younger brother John in line to make his NSW Waratahs debut at Newcastle's McDonald Jones Stadium.

John Folau, in his maiden season at the Waratahs after switching codes from rugby league, was promoted to the bench on Thursday after winger Curtis Rona was ruled out with a groin injury.

While Alex Newsome will start as Rona's replacement, the 24-year-old Folau is almost certain to be unleashed on the Sunwolves at some point in the second half.

A former Queensland under-20s rugby league representative, Folau played one Test for Tonga in the 13-man code and three NRL games for Parramatta before joining Israel at the Waratahs in the off-season.

Waratahs assistant coach Chris Whitaker, who also coached Folau in last year's National Rugby Championship, is confident the rookie will handle the step up.

"He's taken huge progression," Whitaker said on match eve.

"Before he came in, he hadn't played rugby union before.

"He's obviously watched his brother play so he's learnt a fair bit off his brother.

"But he's been good. He's been in there doing extra hours and just learning positional play.

"Naturally he's an athlete. He's got all the attributes to be a top player. Now it's just about getting game time."

Getting the call-up so late will also help, Whitaker believes.

"He doesn't have the build-up that he would have (had), and the nerves. He's coming in late so I think it will be good for him," Whitaker said.

"He can switch straight back in to it and enjoy it. Just play his natural game.

"Sometimes he's got a tendency to over-think. He's just a natural player that I think he's just got to back himself and his instin cts will just kick in.

"So don't think too much and just play."

Wallabies superstar Israel Folau, who last week joined former Blues and All Blacks winger Doug Howlett as Super Rugby's all-time joint top try scorer with 59 five-pointers, has been a key figure in his brother's transition to the 15-man code.

"They've been pretty good at training. They run at each other and they gee each other up a fair bit," Whitaker said.

"So it's good. I dare say Izzy will look after him on the field and show him the ropes."

AAP