Victory at Lille would put huge pressure on Girondins Bordeaux in the title race, Olympique Marseille midfielder Karim Ziani said.
Marseille lead the standings on 64 points with six games left, with Bordeaux in second place two points behind.
The Aquitaine side, however, play the League Cup final against Ligue 2 side Vannes on Saturday and would be five points off the pace should Marseille win.
"It is a turning point because Bordeaux do not play. They will be under big pressure if we win," Algerian Ziani told sports daily L'Equipe on Friday.
Olympique Marseille will be without captain Lorick Cana for their trip to Lille after the midfielder was handed a one-match suspension for trading punches with Lorient's Arnaud Le Lan on Sunday.
Lille striker Nicolas Fauvergue said his team had put their 2-1 defeat at strugglers St Etienne behind them as they gear up for Marseille.
"After the defeat, we quickly re-focused on our goal (reaching a Champions League spot)," Fauvergue told his club's website.
"We had a video session and swept this defeat out of our minds to get into the Marseille game as quickly as possible."
Lille are sixth on 56 points, three adrift of third-placed Olympique Lyon, who hold the last Champions League qualifying spot.
Christophe Revault, 37, has lost his first-choice keeper spot at bottom club Le Havre to under-21 player Johnny Placide, sports daily L'Equipe reported on Friday.
Le Havre, who have conceded 59 goals from 32 matches this season, host Grenoble.
Toulouse, knocked out by Ligue 2 side Guingamp in the French Cup semi-finals on Wednesday, have a mental problem, said defender Daniel Congre.
"To me, it is a mental problem. There is no such thing as fatigue in a French Cup semi-final," he told L'Equipe before they host Lorient on Sunday.
Toulouse are fifth in the standings on 56 points.
