The Brazilian was one of a host of new arrivals at the Stade Velodrome over the summer, with owner Frank McCourt pumping money into the team in a bid to reinvigorate a previously ailing squad.
Coach Rudi Garcia has engineered a solid start to the season, with Les Phoceens currently sitting fourth in Ligue 1.
Gustavo says he is enjoying the challenge of helping the club get back to their former position, especially as he feels their play reflects the passion shown by their famously vociferous fans.
He said: "The project is very ambitious. Our philosophy is different, our supporters too. They like players who fight. Who live for their club.
"We believe that we must stay in what is the essence of the OM: play ninety minutes thoroughly, fight and that in the end our supporters are proud of us."