Lionel Messi has been suspended for one game after sitting out the MLS All-Star Game without prior approval, the league said on Friday.
The Inter Miami forward and his teammate, Jordi Alba, did not compete on Wednesday despite not being injured, even though they were included in the All-Star roster.
"Per league rules, any player who does not participate in the All-Star Game without prior approval from the league is ineligible to compete in their club’s next match," MLS said in a statement.
The suspension will see Messi, the league's main attraction, miss Inter Miami's match against the visiting FC Cincinnati on Saturday. Cincinnati lead the Eastern Conference standings.
Messi has scored 18 goals so far this season.
"I know Lionel Messi loves this league. I don’t think there’s a player - or anyone - who has done more for Major League Soccer than Messi. I fully understand, respect, and admire his commitment to Inter Miami, and I respect his decision," MLS Commissioner Don Garber said in a statement.
"Unfortunately, we have a long-standing policy regarding participation in the All-Star Game, and we had to enforce it. It was a very difficult decision."
All-Star competitions are a mainstay of North American sports, where the men's "Big Four" leagues use the exhibitions to boost their players' profiles, but a rarity in professional soccer.
"We're going to take a hard look at the policy moving forward. I’m committed to working with our players to determine how the rule should evolve," said Garber.
Inter Miami managing owner Jorge Mas described both players as "consummate professionals" who were "extremely upset" about the suspensions.
He explained that the club made the decision for the players to miss the All-Star game to prioritize their rest and health during a demanding stretch of matches. Mas strongly criticized the rule, calling it "draconian."
"The ones that get penalized are the club, the fans, sponsors, Apple TV, and so on," Mas told reporters during a conference call on Friday.
"I expressed our disagreement with the league's decision, and I had conversations with the commissioner both this morning and late last night," he said.
"But notwithstanding that, the decision is what it is."
Mas added that there was no appeals process available.