Perth coach David Zdrilic says he dropped Cristian Caicedo after the Glory recruit's blow-up over being substituted for his lack of defensive prowess in their previous outing.
Caicedo did not play in Sunday's 2-0 loss to Melbourne Victory at AAMI Park after being left out of the squad altogether.
In last week's 2-2 draw with Adelaide United, the 22-year-old Colombian attacker was brought on in the 59th minute.
He was shocked when he saw his number pop up to be substituted in the 91st and stormed down the tunnel.
"I left him out this week," Zdrilic said.
"What we need from any of the players is that defensively we need to be very strong. That's first and foremost.
"We have to understand that in this moment, particularly in a couple of the games, we conceded way too many goals.
"Defensively is a big focus for us. It always is, but in this situation, I'm choosing players that are going to give us that first."
When pressed on whether Caicedo's omission was due to his defensive work alone or his tantrum, the coach conceded it was "a bit of both".
"But for me, a lot was made of that last week," he added.
"It's very clear and simple for me. Just because a player comes on, doesn't mean they can't come off."
Caicedo could yet return against Newcastle next Saturday.
"If he trains well, everyone's available," he said.
Perth remain winless after seven games under Zdrilic and sit 11th.
The first-year coach stressed the Glory were going through a "total rebuild" that was "going to require patience, not just from the fans, but also from me".
"I'm trying different things. I'm trying to get the best out of the players we have at the moment, and we are going to change a lot of things," he said.
"So, at the moment, we want to manage this situation, keep building the team, and in the background, there's a lot of rebuilding going on.
"I know there's a lot of frustration because everyone's going to look in the immediate.
"But the owners that have come in, and Ross Pelligra and his vision for this club, there's a lot happening that obviously you're not going to see. You're going to see (it) later on.
"But we have to wear the pain now, try to manage it, try and build with what we have, which we are doing."
Zdrilic welcomed the signing of veteran defender Tomi Mrcela but stressed he had to "bring him up to speed".
