Messi gets down to business in first Miami training session
The Argentine World Cup winner took to the club's training field at 9am local time with temperatures already above 30 degrees Celsius (86 degrees Fahrenheit).
Chatting with Venezuelan international Josef Martinez, likely to be his strike partner for Miami, Messi was watched by over 200 media representatives who had attended the session.
Miami's training sessions had barely attracted double figure attendance from the media prior to Messi's arrival.
Messi had been unveiled to the club's supporters at the stadium on Sunday at a celebratory event alongside Miami co-owner David Beckham and his first game is scheduled for Friday.
Miami, who are ranked last in the 29-team MLS, face Mexican club Cruz Azul in the opening game of the new Leagues Cup, a tournament style competition featuring all top flight teams from MLS and Mexico's Liga MX.
It is not clear yet if Messi will start that game or make a cameo appearance from the substitute's bench and his coach, fellow Argentine Gerardo 'Tata' Martino has asked for patience while the 36-year-old builds up his fitness.
Messi has not played since his final game for Paris Saint-Germain in the French league on June 4 and would normally be entering the pre-season phase at this time.
Unlike in most of Europe, MLS's season runs from late February to the end of October, followed by the playoffs and the championship game, MLS Cup, on December 9.
Despite sitting rock bottom of the Eastern Conference with the worst recording in the league, Miami are not mathematically ruled out of contention for the playoffs but it would take a huge impact from the seven-times Ballon d'Or winner to turn their season around.