For the first time since August 2011, Messi has failed to score in his last four league games - finding the net just once in October.
The Argentine has struggled with a thigh injury in recent weeks and Martino has put his dip in form down to the forward not being 100% fit.
"Messi isn't troubled by this," Martino told the BBC. "Injuries happen. To Messi, or anyone.
"It's a coincidence that Messi hasn't scored in three or four games, he's not desperate.
"He's set the bar so high that it seems when he doesn't score it's a problem."
Messi is expected to start in Barca's Champions League clash against AC Milan on Wednesday night.