The Wallabies flanker wants to see his club teammate start at number 10 in Sydney next week.
Mo'unga is in contention for the All Blacks' No.10 jersey after being a shining light for the Crusaders this season.
The Crusaders have won their ninth Super Rugby title, defeating the Lions 37-18 in front of their home fans in Christchurch.
Scott Robertson said his No.10 played exceptionally and admitted the forwards were on another level against the Lions.
Asked how the 202-cap prop took the news, Robertson said: " It wasn't an easy conversation. We reconvened the next day."
The Crusaders winger put his opposites to shame in his side's 30-12 semi-final win over the Hurricanes in Christchurch, writes Campbell Burnes.