Nabil Fekir scored a 67th-minute winner for Lyon as they edged to a 1-0 win at home to Nantes on Sunday, much to Fournier's relief.
Fournier said Lyon were entering a decisive period, with matches against Lille, Montpellier and Marseille coming up away from home.
But he feels the title is still PSG's to lose, with Laurent Blanc's men sitting second in the league.
"I think that our next three games away in a row, starting with the one against Marseille, will say if we have a chance to clinch the title or not," Fournier told a media conference.
"Then after Marseille, we will have to travel to Montpellier and Lille. We will then know what we can expect from this season, as we will be very close from the final sprint.
"We will know if we can still compete with PSG, even if the title has always been theirs to grab since the start of the season.
"If Paris Saint-Germain wins the title, it will make sense. But we'll try to make it as hard as possible for them."
Fournier talked up the importance of Sunday's win, hailing Lyon's patience and determination.
"It is a relief. It was a tough game. We fought hard to get a victory because we faced a very well-organised team in Nantes, they were very compact as we expected," he said.
"They didn't give us much space to play. We had to show patience and determination to get these three points."
