Messi's season has been disrupted by thigh and hamstring injuries, although he has still scored 14 goals in all competitions to help Barca lead the way in La Liga and into the knockout stages of the UEFA Champions League.
Ahead of Sunday's trip to second-bottom Real Betis, Martino admits he is unsure how long it will take the 26-year-old to be back to his imperious best.
Martino said: "He had two different injuries and it delayed him to be totally ready to play without problems.
"He is looking for the excellence.
"How long is it going to take? With Leo everything is really unpredictable.
"When I was questioned about it after we played Real Madrid, just three days later he plays a great match against Milan.
"That can happens anytime regarding Leo Messi."
Betis have lost four of their last five league games, but Martino is reading nothing into recent form.
He added: "I expect a match where the rival starts in the aim to get the victory, as Betis usually do.
"They have really good players.
"Although they aren't getting good results in La Liga, they're doing well in Europa League so we're aware that it will be a really tough match and we'll have to do our best to get through this match."
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