The promoted principality club have started strongly following their extensive - and expensive - summer recruitment, with two wins and a draw from their opening three games.
That still leaves them two points behind Elie Baup's side, though, and Ranieri is well aware of the task which awaits his men.
"Marseille are a good team, they play in the Champions League and for us this will be a real test," he told the club's official website.
"I want to see how my players do against this kind of team.
"What matters to me is to play and win as a team. I hope that will be the case on Sunday."
One of those summer recruits, Portugal playmaker Joao Moutinho, is in line for his Monaco debut following a thigh injury and Ranieri hopes that will benefit another, Moutinho's former Porto team-mate Radamel Falcao.
"Moutinho should play," said the Italian. "We will see how he feels after the final training session.
"I think with Moutinho in the team, Falcao will have more chances because they are used to each other."
Monaco have also added to their midfield options with the capture of France international Geoffrey Kondogbia from Sevilla for a reported 20million euros.
Marseille's 100 per cent start to the league season saw four of their players included yesterday in France's squad for their World Cup qualifiers against Georgia and Belarus.
That includes a first call-up since the 2010 World Cup for striker Andre-Pierre Gignac, to the delight of club and country colleague Mathieu Valbuena.
"I congratulate him, it is to his credit," Valbuena told the club's official website.
"He has worked quietly since he came here and he is now harvesting the fruits of that work. I hope he will put together good performances for OM and France.
"To have four OM players in the France team is very encouraging for the club and that can only help our togetherness on the pitch."
One player who has not shone in the club's stellar opening is Cameroon defender Nicolas Nkoulou, whose error gifted Guingamp their consolation goal in last week's 3-1 scoreline.
"I cannot explain my difficulties, I can't say whether it's because I returned late (for pre-season) or something else," he said.
"My error at Guingamp, I had forgotten it by the next day.
"I am working to be able to give what people expect of me."