The Wallabies endured their worst test campaign in 60 years in 2018, winning four out of 13 matches and slumping to sixth in the world rankings.
However, former scrumhalf Gregan, who scored 99 points in 139 internationals, believes Michael Cheika's men can peak come tournament time in September, just as they did in 2015 when they reached the final.
"They do have time in a World Cup year, which is a unique year. It is about getting it right when you get over here," said Gregan in an interview with Reuters in Sapporo.