Messi has eight goals in eight La Liga appearances this season but has gone two league matches without a goal – including against Real Madrid on Saturday – and questions were raised over his performance in El Clasico.
The prolific Argentinian only had three shots at goal, and failed to test Madrid goalkeeper Diego Lopez with any of them, also completing just 77 per cent of his passes.
Martino remains happy with the 26-year-old's performances and hailed the work he does to help the team.
"I'm not worried about Messi, that's more something from people outside," the former Paraguay coach said. "Even if he doesn't score, he's important for the team.
"He can play at different positions and that's a good thing for the team
"If with his current stats, journalists think Messi isn't doing well, I guess his stats will be out of this world when he's good."
Victory over Madrid saw Barcelona move six points clear of their rivals after 10 rounds, but Martino was quick to dampen any talk of the title and insisted his side will maintain their focus.
"You win the league game by game," he stated. "You can't relax. We should continue to improve every match.
"Winning El Clasico is always a mental boost for the players. The mood can't be better.
"Until numbers say otherwise, Madrid are a rival for the title.
"Atletico is doing perfectly, I have said it before they're a candidate."
Barcelona face two games in the next four days against Celta Vigo and city rivals Espanyol.
