PSG has struggled recently with two ties in Ligue 1 play and a loss in the Coupe de France.
Although undefeated in 14 straight Ligue 1 matches since early December, PSG's title hopes are being threatened by surprise Montpellier.
Montpellier took advantage of two straight PSG ties to move to the summit with a 1-0 win over St. Etienne last week, but have a bye this week after its match with Marseille was postponed.
With its lead only on goal differential, Montpellier can do nothing to prevent PSG from claiming the top spot this weekend when it visits Nice.
Even a tie will move Carlo Ancelotti's club atop the standings and, if nothing else, put pressure on Montpellier when it returns to action.
After last week's second straight draw, Ancelotti was not pleased.
"I'm not happy. We wanted to win. We're not in a good spell right now. It took us a long time to get into the game," Ancelotti said last week after a 1-1 tie against Bordeaux.
"We again waited for the second half. It was only then that we put on more pressure and took control, but we made mistakes in defense."
PSG spent well over $100 million combined in the summer and winter transfer windows, but has just one chance at a title this season: Ligue 1. PSG has been knocked out of its other competitions, including the Europa League.
With just nine matches left this season, PSG faces a crucial step as it tries to return to Ligue 1 dominance. PSG last won the title in 1994.
"We need more confidence, more discipline," Ancelotti said, "and we need to play simpler football. We have to work harder."
Nancy sits just 12th in the table, but has three wins during its current four- game unbeaten streak. In addition, it is just five points above the relegation zone, and must continue to pick up points to secure its safety.
Defending champion Lille has won its last two games and sits third, which will be enough to make the qualification stage of the Champions League next season.
But with Montpellier and PSG well clear, Lille will face a huge challenge down the stretch for its coveted place in the table. Lille hosts Toulouse on Sunday in a battle of third- and fourth-place teams.
"If we keep winning, we know that our position in the table will be good," said Lille coach Rudi Garcia. "There are still 27 points to be had, and effort to be put in.
"We're going to focus on our match with Toulouse, which is another important game. If we maintain this desire and determination, we can have a lot of hope for the end of the season."
Lyon has won four straight in all competitions, three matches in Ligue 1 and against PSG in the Coupe de France, since its Champions League elimination and visits Rennes on Sunday. Lyon is just four points behind Lille in fifth.
Also Saturday, Auxerre hosts Valenciennes, Bordeaux hosts Dijon, Lorient hosts Evian, Sochaux hosts Brest, and St Etienne hosts Nice. Also Sunday, Caen hosts Ajaccio.