Ever since arriving at the MLS side, Messi has put together an influential run of form, contributing 11 goals and five assists from just 11 appearances.
Despite their struggles in MLS, Inter Miami have won the Leagues Cup with Messi in their side, and also find themselves in the final of the US Open Cup.
However, the 36-year-old now appears to be a huge doubt to feature in next week's showpiece against Houston Dynamo having been forced off during the first half versus Toronto.
The former Barcelona and Paris Saint-Germain star had been making only his third outing in the league before he exited the game in the 37th minute.
Messi's withdrawal came just two minutes after Jordi Alba was substituted, also with a fitness concern, yet Inter Miami still went on to post a 4-0 triumph over the Eastern Conference's bottom-placed team.
After the game, head coach Gerardo Martino was naturally quizzed on the issue, ruling Messi out of the next MLS game at the weekend and indicating that he faces a race against time to recover for the clash with Houston.
Speaking to reporters, as quoted by BBC Sport, Martino said: "There is no chance they will be there on Sunday.
"I know we have a final to play [on Wednesday] but they won't go near the pitch if they can't play."
Messi had missed Argentina's second fixture of the international break and the 5-2 defeat to Atlanta United last weekend before being brought back into the team.
Martino added: "The scans [Messi] had with the national team, they didn't show any injury. We still saved him to be safe.
"We don't think he has a muscular injury. That's also from a conversation I just had with him. But we have to continue being careful. We'll look at it the next few days."
Since his summer transfer, Messi has only participated in half of Inter Miami's six MLS fixtures, although the team is still in contention for the playoffs with a six-point gap to the Eastern Conference playoffs with a game in hand.