The 31-year old has walked out on the club after he was denied a deal to join Sydney FC for the upcoming Asian Champions League.
Reds boss Rini Coolen said he had every right to deny Reid that opportunity as the club is bigger than the player as they prepare for tomorrow night's knockout clash with Wellington Phoenix at Hindmarsh Stadium.
"We told him we don't allow him to go (to Sydney)," Coolen said.
"And I think everybody can understand - our club, our sponsors, our team, our supporters - that we can't do that because we have to prepare ourselves for big games, so we can't lose him, he's important in our squad.
"And he was real disappointed about that, more yesterday, and he asked me not to pick him in the squad, he couldn't focus for the game.
"That gives me a real big problem and also a big disappointment to be honest, I think it's not professional."
Coolen added that the distraction had not wrecked the players' focus.
"It's always a disappointing moment when you lose a person, it doesn't matter who it is ... it's not good if you have something like that," he added.
"This is something you don't want ... anyway, it happens.
"The team is focused, they trained well, they can handle it - they have to handle it because we are professionals and we have to be ready tomorrow so we don't want to use it as an excuse."
Reid's departure opens the door for Adelaide vice-captain Lucas Pantelis to grab a starting position after coming on as a sub in his last six matches.