A match-up between Britain's Fury and the American has been postponed twice already.
Last week it was announced the rescheduled fight would take place in Riyadh on 26 February.
"A part of me definitely still doubts," Paul, 26, admitted.
"It's scary and it's annoying, and the kid's not necessarily reliable but the money's good, for him, so he would be just so dumb."
And referencing Fury's relationship with social media influencer Molly-Mae Hague, Paul added: "I think he's probably tired of Molly making all the money in the relationship."
A planned bout in New York in August was called off after Fury was denied access to the United States.
Fury, 23, also withdrew from their fight in December 2021 through injury.
Paul said American mixed martial artist Mike Perry was on standby: "He's ready to jump in, in case Tommy pulls out."
Paul and Fury faced off in the ring before Anthony Yarde's light-heavyweight defeat by Artur Beterbiev in London on Saturday. Speaking after the bout, the viral content star turned fighter explained why he was desperate to fight Fury: "I want to make him pay, he wasted my time multiple times. I want to take his career away from him," he said.
Fury is the younger brother of world heavyweight champion Tyson and Paul said Tommy was a "Fury family puppet" who "feels he has to live up to that" so was "saying things I don't think he believes" about the outcome of their fight. "He's in for a rude awakening," he added.
However, he did praise Fury's credentials as a professional fighter - he will be the first professional boxer Paul has faced in his short, six-fight career to date.
"I'm validated. I've done everything I needed to do in this sport for me personally, I've proved everything to myself but it will be nice to take on a professional boxer, one with a big name, a tonne of credibility.
"He's been fighting since he was 10, 11 years old and I've only been doing this for three years.
"It's another stepping stone because I want to become world champion. I want to and I will. I'm capable of it and no one's believed in me.
"When I said that four fights ago people laughed, they don't want to believe that's possible because of my background, but I believe anything is possible if you set your mind to it and dedicate your whole entire life and have a little bit of natural talent, which I happen to have."