The Inter Miami superstar has been suspended for the MLS clash with FC Cincinnati.
The ruling has been made after Messi snubbed MLS All-Stars selection, citing "fatigue". Inter Miami teammate Jordi Alba has been handed the same suspension after also rejecting his All-Stars call.
Messi is said to be furious with the ban, which has been blasted by Inter Miami owner Jorge Mas.
Garber said this morning: "It was a very difficult decision.
"I know Lionel Messi loves this league.
"I don't think there's a player - or anyone - who has done more for MLS than Messi. I fully understand, respect, and admire his commitment to Inter Miami, and I respect his decision.
"Unfortunately, we have a long-standing policy regarding participation in the All-Star Game and we had to enforce it."