The 21-year-old's move from Santos to Camp Nou was the subject of heavy scrutiny in January, resulting in the resignation of Barca president Sandro Rosell amidst fraudulent tax claims from the Spanish government and threats of legal action in Brazil.
Although Martino thinks part of the reason Neymar struggling is his recovery from a sprained ankle, the Argentine coach also suggests off-the-pitch issues have impacted the Brazilian.
"His position on the pitch hasn’t changed much since his return," he told reporters. "As a left winger or centre forward his performances have been very good."Against Manchester City he played out right and he was very good. He’s fine playing in any of the three positions up front. Coming back from a month out it’s always hard to get your rhythm back and then all the difficulties with his signing came up.
"If I had to choose a reason I’d say it was from things off the pitch."
Barca have lost ground in the race to defend their title after recent defeats to Real Sociedad and Real Valladolid, with next weekend's trip to leaders Real Madrid now looking like a game they cannot afford to lose.
And Martino is glad to have a full week to prepare for the Clasico following Sunday's clash with Osasuna, suggesting that victory this weekend is essential to prevent a potential seven-point gap from opening up between them and Carlo Ancelotti's men.
"To have the whole week off good bad that we've got a full week available, it's how you prepare for it," he added. "There aren’t any magic words or magic talks, there are reasons to keep fighting though things are no longer in our hands.
"Tomorrow’s game is very important in terms of what’s coming up next week. Osasuna is key if we’re still to have a chance against Madrid."