Messi's current deal expires at the end of the calendar year and talks over a new contract continue to drag on.
But Mascherano said of his former Barcelona teammate's situation: "I see him as very happy. I think he's found the ideal place to relax and enjoy many things he couldn't experience elsewhere. Ultimately, he'll decide, but today I see him as truly calm and happy."
Ahead of their clash with New England Revolution, Inter Miami's coach also said: "Even with the best squad in the world, if you give Leo a rest, his absence is noticeable. But this year we've played several games without him, and everyone has stepped up to compensate for his absence.
"Messi knows how to manage himself like few others. I don't want to promise anything; we'll decide day by day based on how he feels."