The big-spending capital side, knocked out of Europe's premier club competition by Real Madrid in the last 16, have virtually wrapped up the Ligue 1 title as they lead second-placed Monaco by 17 points with seven games left.
The teams meet in the League Cup final on Saturday, but PSG's big objective this season was the Champions League.
"First they need to win the League Cup and then enjoy themselves until the end of the season," Fournier, who helped PSG win their only European title in 1996, the former Cup Winners Cup, told Reuters.
Fournier was named PSG coach in February, 2005 but was sacked midway through the following season.
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Asked if PSG should give young players an opportunity to shine, Fournier said it would be a risky option.
"You have to respect football and the clubs who still have something to play for in this league," he said.
"Some clubs will be fighting against relegation and PSG should be careful not to distort the championship.
"They need to field the best possible team for each game, especially since they have records to chase," the former France international added.
They are 13 points short of their own French record of 96, set in 2015-16, and could establish a best mark for goal difference, which they did in 2015-16 with plus 83. They are currently on 73.
One record they will find harder to break, though, is for goals scored, having found the back of the net 95 times while RCA Paris netted 118 times in the 1959-60 season.
The players, however, should still be motivated with the World Cup looming and victory on Saturday would earn PSG their 40th consecutive win in domestic cups going back to January, 2014.
"Some of them could use the end of the season to gain confidence for the World Cup," Fournier said. "Apart from that they should have fun."
(Reporting by Julien Pretot; Editing by Ed Osmond)
