Dorigo, 55, who won the league title with Leeds under Howard Wilkinson in 1992, expects Bielsa to stay for another season.
But the former England left-back admitted there was room for doubt due to Bielsa's preference to sign 12-month contracts, the last of which he signed the day before the current campaign began.
"Marcelo's successor has always got to be planned for, whenever it comes," Dorigo told the PA news agency. "It is going to come at some point.
"I hope that's a long time in the future, but realistically they have to plan for it and it's going to be a tough one because of the complete change in style.
"He's not like many other managers out there. He won't easily be replaced."
Leeds fans have endured anxious waits at the end of Bielsa's previous two seasons at Elland Road and chairman Andrea Radrizzani has made clear in several interviews that should the Argentinian move on, the club would have plans in place.
"That is going to be a tricky one, but I'm sure they are on the case," Dorigo said.
"They'll be watching and ear-marking and that's what they have to do because what is vital is that Marcelo Bielsa has got them into the Premier League, there's a nice platform, but they have to build and stay there for a long time."
Dorigo, currently working as a co-commentator on LUTV, said he had a hunch that Bielsa will remain for at least a second season in the top flight.
"Is it a foregone conclusion? No. I'd be really surprised if he does leave, but you can never be certain," Dorigo said.
"What is important is that the club understand the type of manager they have got. They try to give him all the tools to enjoy his job and do the best he can."
Leeds took a huge risk when making Bielsa the highest paid manager in the club's history in 2018 on a reported £6million salary package, which covers his wage and those of his assistants and backroom staff.
Dorigo feels it has been money well spent. "There's no doubt that in two-and-a-half seasons he's turned the club on its head," he said.
"It's a completely different place to play, work and watch and it's very much down to him and of course Andrea Radrizzani, for spending and gambling.
"It was a gamble. It was a lot of money for a manager in the Championship, but it has turned out fantastically well and I still think there is more of the story to run."