Marseille has proven in its two European matches it is one of the best teams in France, but when it comes to Ligue 1 so far this season, the 2009 champions are struggling.
Despite wins over Olympiacos and Borussia Dortmund in the Champions League, Marseille has just one win in nine Ligue 1 matches and has already fallen 12 points off the pace of PSG.
Marseille visits fourth-place Toulouse on Saturday, when Benoit Cheyrou said the club's fortunes need to take a turn for the better.
"We've made a very poor start to the season and we need to start making up for it," Cheyrou said. "We're all completely concentrated on that match. Toulouse is a very physical side who use the ball well.
"They've had a great start to the season. It'll be a tough match."
Toulouse has five wins and two draws from nine matches, and is tied with three teams on 17 points behind PSG.
But Marseille, which is just three points off the bottom of the table, can use its Champions League success as an example to launch its domestic campaign and look back on 2007-08, when it struggled early but recovered to finish third.
That season, Cheyrou's first at the club, Marseille was 19th after 13 matches, but climbed into the top three to qualify for the Champions League playoffs.
"Despite this terrible start, we managed to finish the season in third place by blitzing our opponents in the home stretch. We did it five seasons ago, and we can do it again this time around," Cheyrou said.
"Mathematically, it's doable. I have hope, and when you have hope, you can move mountains. It'll be tough, but it's possible."
Cheyrou did acknowledge Marseille needs to perform as a team, and that was the only way it could erase its early-season struggles.
"We need to perform out on the pitch and fight hard," Cheyrou said. "It's not through individual brilliance that we'll get ourselves out of this jam. We're all in the same boat and we all need to step up.
"We're all responsible and partly to blame for the situation we're in - if not, we wouldn't be in it."
Marseille will have to deal with the absences of defender Cesar Azpilicueta, and midfielders Alou Diarra and Mathieu Valbuena due to suspension, making the trip to Toulouse even harder.
PSG, meanwhile, will try to continue its impressive form at Ajaccio on Sunday. PSG, which spent well over $100 million on transfers this summer, lost to open the season, but has gone unbeaten in its last eight - including six wins.
Second-place Montpellier hosts Dijon and third-place Lyon hosts Nancy in two Saturday matches, while Auxerre hosts Lille, Brest hosts Caen, Evian hosts St Etienne, and Nice hosts Bordeaux in the day's other games.
Also Sunday, Valenciennes hosts Sochaux and Rennes hosts Lorient.