Fresh from last night’s heartbreaking Asian Champions League (ACL) exit, Arnold said major surgery was needed before next season.
He expected “another five or six” of his squad would follow already-departed cousins Jacques Faty and Mickael Tavares out the door.
The Sky Blues’ 2-2 second-leg draw with Shandong Luneng at Allianz Stadium ended a successful run in the ACL, a tournament in which they’d flourished despite failing to make the A-League finals.
The coach will now turn his full attention to rebuilding a team that made the grand final only a season ago.
“The worst part of my job is telling players they’ve got to leave or move on,” Arnold said.
“We’ve had an exceptionally good Champions League, but clear in my mind is the A-League.
“There’ll be changes. I have to look at how to get this club to the top.
“Hard decisions need to be made, and they will be made in the next day or so.
I have to forget about developing kids. It’s what I love, but I’ve got to forget about it.
“And then recruitment. We’ve already started obviously with (Michael) Zullo and (Alex) Wilkinson, but there’s probably another four or five that will come in.”
Sydney have already secured the signatures of Melbourne City pair Zullo and Wilkinson and are on the hunt for a striker to boost their underwhelming attack.
Skipper Alex Brosque’s likely move under the salary cap from his marquee spot will free up space for a high-profile name in that role.
Arnold also made the surprising admission that he would stop nurturing young talent – his signature – in order to make the Sky Blues more competitive.
“I have to be more ruthless,” he said.
“I have to forget about developing kids. It’s what I love, but I’ve got to forget about it.
“I’ve got to get the best players I can find, and if that means I’m like a lot of the other clubs where I don’t have any kids, that’s what I have to do.
“It’s always something I’ve really enjoyed developing, and I watch the Socceroos squads and there’s five or six players I helped.
“But I can’t do that anymore. I have to think about what needs to happen to win.”
Arnold felt Sydney’s round-of-16 loss to Shandong was more painful because the 3-3 aggregate loss was decided on away goals.
He questioned the penalty conceded by red-carded Zac Anderson, suggesting the player he’d denied a goal-scoring opportunity, Yang Xu, had been offside.
But even despite goalkeeper Vedran Janjetovic’s class in saving Diego Tardelli’s spot-kick less than 15 minutes from time, Arnold said he never allowed himself to believe it was Sydney’s night.
“I’ve been in football long enough to know it’s not over until the final whistle,” he said.
“I knew they’d keep coming at us and I didn’t have any defenders on the bench.
“With Seb Ryall out we didn’t have any back-up defensively.”
Help our journalists uncover the facts
In times like these InDaily provides valuable, local independent journalism in South Australia. As a news organisation it offers an alternative to The Advertiser, a different voice and a closer look at what is happening in our city and state for free. Any contribution to help fund our work is appreciated. Please click below to donate to InDaily.