The 37-year-old Argentine striker suffered a right ankle injury in his nations victory over Colombia in the Copa America final this month.
Messi missed two MLS matches last week and Wednesdays MLS All-Star Game against Mexicos Liga MX All-Stars.
Martino said Messi remains in a walking boot as he works with club trainers but the ankle is getting better and better, according to the Miami coach.
Last year, Messi arrived at Inter Miami and led the club on a title run in the inaugural edition of the Leagues Cup, which features MLS and Mexican clubs in a World Cup-style format.
There are 15 three-team groups in the first round and two from each will advance to the knockout stages along with the reigning league champions, Club America and the MLS Columbus Crew.
