Rookie Apisai Koroisau will be thrust into the cauldron of an NRL grand final in just his 14th first grade game, after “devastated” South Sydney hooker Issac Luke was rubbed out of the 2014 decider against Canterbury on Sunday.

The NRL judiciary upheld Luke’s suspension for a dangerous throw on Tuesday night.

Koroisau, who will join Penrith next season, will now wear the Rabbitohs No.9 at ANZ Stadium in Souths’ first grand final in 43 years.

Koroisau is a similar style of running dummy half to Luke and the 21-year-old capably filled in for the Kiwi rake earlier this season when he was sidelined with a shoulder injury.

Luke was outed due to a grade one dangerous throw on Sydney Roosters back-rower Sonny Bill Williams in the Rabbitohs 32-22 preliminary finals win over the premiers on Friday.

The 27-year-old will also miss New Zealand’s opening game of their Four Nations campaign against Australia in Brisbane on October 25.

Koroisau has previously praised Luke for helping him to improve his own game and Luke is confident his understudy can get the job against the massive Bulldogs pack.

“Devastated but at the same time excited to still be part of this amazing journey. Time to rip little brother @apikoroisau,” Luke wrote on social network platform Instagram.

“I got your back g.”

Canterbury will also be missing their first choice rake Michael Ennis due to a foot injury.

Josh Reynolds and Moses Mbye are expected to share the hooking duties for the Bulldogs.