"Out of the current champions of the four organisations, Wladimir Klitschko, Ruslan Chagaev and Deontay Wilder, Wilder is probably recognised as the weakest of the three," Lonergan said.
"That's what makes the Fujimoto fight so valuable to us - a victory over him will put Joseph on course to fight Wilder and that's why I've been chasing [Fujimoto] for over a year."
Parker extended his undefeated professional record to 14 victories when stopping Saglam early in the second round in front of a noisy crowd of 3000 at Arena Manawatu.
It was Saglam's fourth defeat in 38 fights but he was completely outclassed by a 23-year-old improving with every outing.
"He's a world-class fighter with world-class power. Not many heavyweights in the world have the shocking power that Joseph Parker has," trainer Kevin Barry said afterwards.
While Fujimoto has a 12-win, one-loss professional boxing record, he is unlikely to last the distance against Parker, who believes he has gone to the next level after his recent training camp with Klitschko.
The fight at Stadium Southland will be a special occasion if Saturday's at Arena Manawatu is any indication.
The applause as Parker walked to the ring was among the loudest the South Aucklander has encountered - he later said it was the best crowd he has fought in front of.
"That was awesome, Parker said. "The crowd, the buzz, the atmosphere, got me excited."
It vindicated promoters' Duco's decision to take Parker to the regions.
