The forward described losing to Belgium in the quarter-finals of Russia 2018 as the "the saddest moment" of his career, having scored twice in five games at the tournament and drawn criticism for his play-acting.
Neymar missed the end of the 2017-18 season with a fractured foot as PSG won a domestic treble in his first season in the French capital after joining from Barcelona in a world-record €222 million deal.
And Buffon thinks failing to win the World Cup could act as extra motivation for Neymar in the coming campaign.
"I think that it happens to everyone to get difficult moments," Buffon said at his presentation to the media on Monday.
"In life, first of all, and during our careers. But there are moments that make us stronger.
"Neymar can come back in Paris with the envy to win everything. It's a good thing for him and the club."
"I played only a year with him but I have affection for him," said the veteran goalkeeper. "He told me, 'In my opinion, Paris need a person like you, you'll feel good there'. That's why I listened to his advice.
"PSG are the team that I followed the most in recent years because I was curious. I was surprised to see that they couldn't reach their objective. But the team needs time, we always need time to improve.
"Paris have great ambitions and there is a constant progression. I think that the team has the character of the coach."