Martino believes that Messi is simply struggling to match his high level of performance at the start of the season, which saw the Argentine score nine goals in Barca's first four matches.
He told AS: "I keep saying the same thing, I keep having to do an exclusive analysis of him in every game. He is the most important player in a team full of amazing players. He plays in his own way and offers us what he offers.
"I do not think he's worried. In reality, I've seen him make the same facial expressions throughout his career. It's just a coincidence. In the same way it was strange to see him score in 19 consecutive games [last season].
"Also it's strange that he has not scored in three games. Of course I would have been delighted for him to keep scoring two, three or four goals per game. In September he set the bar so high that now it seems as if there is a problem. But in my opinion, there's no problem."
Victory over Espanyol took Barca four points clear at the top of La Liga, with 11 wins a draw from their first 12 matches.