Marcelo Bielsa's men sit two points behind leaders Lyon through 23 matches.
Fanni said Ocampos, 20, comes to the Stade Velodrome with youthful exuberance and motivation to perform well, after joining Marseille on loan from Monaco on Monday.
"He [Ocampos] looks very motivated. He will bring a lot of energy to the team," the veteran right-back said.
"It's always good to have highly motivated players. They give their maximum. It pushes others to be better. And technically he looks comfortable. It can be good for us."
Marseille have taken just one point from their past six away trips in the league, something Fanni said had to change ahead of their visit to Rennes on Saturday.
"We need to win away, in Rennes or elsewhere. The sooner the better," said Fanni, who returns to his old home ground at the weekend.
"If we want to be on the top of the league, it's important to win games away.
"Against Rennes or against another team, we will have to show a lot of ambition if we want to finally win away."
Fanni also defended the behaviour of maverick PSG striker Zlatan Ibrahimovic.
"I feel that it is a role of arrogant guy is one he [Ibrahimovic] is given, and he does it very well because we talk about him a lot," the Frenchman said.
"Maybe we have to give him an Oscar.
"I know some players in Paris Saint-Germain, and they didn't tell me the same thing about him.
"It is a different story, he is not like that."
