Martino was a happy man after watching the Argentines open their Group D campaign with a convincing 2-1 win on Monday over reigning Copa America champions Chile, a result that should ease their passage into the quarter-finals.
Goals from man-of-the-match Angel Di Maria and Ever Banega secured the points for Argentina, who left the injured Messi on the substitutes bench at Levi's Stadium as he recuperates from an injured back.
Martino revealed the 28-year-old FIFA World Player of the Year could be fit to return for Argentina's second group game against Panama at Chicago's Soldier Field on Friday.
"He has continued working here, he's kicking the ball better now," Martino said.
"We expect in four days he'll be in a condition to play. So we're thinking we will be in a better position by then."
Although Messi's replacement, Benfica's Nicolas Gaitan, performed well on the right side of Argentina's front three, Martino is not discounting the importance of their absent talisman.
"We're always a better team when Messi is in the team," Martino said.
"Our chances of winning the Copa are always going to be higher when he's playing."
Argentina struggled in their first three 2018 World Cup qualifying matches last year when Messi was absent with a knee injury, posting a loss and two draws.
Martino however believes his team is learning how to adapt in their captain's absence.
"It's important to respond the right way when he's not there," Martino said.
"Today we came with 23 players and all of them contributed. We showed virtue as a team."
Meanwhile, Chile coach Juan Antonio Pizzi shrugged off suggestions that his team was in a slump after what was a third consecutive defeat following recent friendly losses to Jamaica and Mexico.
"During the course of the game I did not notice a big difference between the two teams," Pizzi said.
"What happened is that we made crucial mistakes and they cost us two goals."
Pizzi is confident that Chile's star-studded team will be able to recover and qualify from Group D, which also includes Panama and Bolivia.
"I trust in my abilities and the abilities of the team and we're going to get up and get back to winning," he said.
"We believe we're going to get into the next round. I know we have difficult games ahead of us. We're going to continue working and we have the belief to move to the next round."
IMAGE: Lionel Messi of Argentina was ruled out due to injury, as he sits on the bench against Chile in 2016 Copa America.
Photograph: Thearon W. Henderson/Getty Images.
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