Miami lost 3-0 in the final at Lumen Field in Seattle.
A melee involving both sets of players broke out, with Suarez grabbing Sounders midfielder Obed Vargas before spitting on security director Gene Ramirez.
“It was a moment of much tension and frustration, where just after the game ended things happened that shouldn’t have happened, but that doesn’t justify my reaction,” Suarez wrote on Instagram.
“I made a mistake and sincerely apologise.
“It’s not the image I want to give in front of my family, that suffers because of my mistakes, in front of my club, that also doesn’t deserve seeing themselves affected by something like this.”
Suarez was given an eight-match ban by the Football Association in 2011 after being found guilty of racially abusing Manchester United defender Patrice Evra.
He has served three bans – at Ajax, Uruguay and Liverpool – for biting an opponent.
