Charles Leclerc has the ability to create a "mess" at Ferrari this year.
"I do not see big changes. The engines are the same. There are some changes to the aerodynamics but I don't think they are big enough to make a difference," Villeneuve told Corriere della Sera newspaper.
The "big change", he said, is the arrival of Leclerc at Ferrari.
"We will have to see what happens," said Villeneuve. "If he were to start immediately strong, it could create an involuntary mess with Vettel. Just like with Ricciardo a few years ago."
He is referring to Red Bull in 2014, where despite his four consecutive titles, Vettel was beaten by team newcomer Ricciardo.
"He (Ricciardo) didn't arrive to make a mess," Villeneuve said. "In theory, Vettel was the favourite but things can sometimes turn against you on the psychological level and you don't know why."
So the Canadian thinks Vettel's only strategy must be to be "strong all season" this time around.
"A lot will depend on the comparison with Leclerc," said Villeneuve. "He knows that if things do not go well, the future at Ferrari will no longer be his but Leclerc's. The pressure is all on him.
"Seb has everything to lose, Charles nothing."
As for reigning champion Lewis Hamilton, Villeneuve thinks he could win a sixth drivers' title in 2019 "If he does not fall asleep".
"Last year, from Germany onwards he was always awake and did nothing wrong, but it's true that his teammate was not there," he said, referring to Valtteri Bottas.