Postecoglou had been expected to fill his final visa spot with a central defender, but will now seek a forward after the surprise exit of Kewell due to family reasons
Melbourne Victory coach Ange Postecoglou says the club will look abroad to replace departed marquee forward Harry Kewell.
Kewell unexpectedly quit the Victory after just one season to remain with his family in England, where his wife's mother is gravely ill.
Postecoglou said while he was disappointed to lose the Socceroos star, he accepted the decision and will look overseas to fill the void.
Initially, he had been expected to use his final overseas spot on a central defender, but Kewell's departure has forced a rethink.
"It's not just about getting a name, he's got to fit into the structure of what we're doing and the kind of player that we want to bring to the club," Postecoglou said on Monday.
"I don't think there'll be an easy local or Australian solution to the kind of player we need.
"Harry was a fairly unique individual. He's had the highest profile of any Socceroo in the last 30 years and maybe ever.
"That's hard to replicate in another Australian player."
Postecoglou said he felt the Victory faithful were yet to see the best of Kewell, who scored eight goals in 25 matches last season after arriving amid great fanfare in August 2011.
"I've always said with foreigners - and I treated Harry as a foreigner because he hadn't played football in Australia before - when you come to this league it's usually the second year they tend to get comfortable and understand how the league works," Postecoglou said.
"I was very confident that Harry would have played his best football this year.
"The team struggled last year, and as a striker and an attacking player, when your team struggles it's very hard to stand out.
"In many respects he did the hard work and laid a foundation last year but unfortunately he can't reap the rewards."
Postecoglou said the recruitment of Kewell was a worthwhile investment and he was confident the former Leeds United, Liverpool and Galatasaray player will continue to feature at international level.
"I don't know him that well, but I reckon he's got the next World Cup in mind as a possibility to still make an impact," Postecoglou said.
"From an Australian point of view it's really important that where he goes he gets comfortable quickly and is successful, because I think he's still got a role to play at national-team level."
Kewell now looks set to continue his career in northern England, where his family are based, and had reportedly been training with Championship side Blackburn Rovers.
Victory also announced on Monday the appointment of former Socceroo Paul Trimboli as football operations manager.
Melbourne-born Trimboli, who worked alongside Postecoglou in a similar position at championship-winning Brisbane Roar last season, said he was excited by the opportunity to return to his hometown.
"Melbourne Victory's fans are quite remarkable and they crave success, so it's a great challenge and one that I'm extremely excited about," Trimboli said.
"Ange and I have known one another for a very long time, so to be able to continue working alongside him - albeit at a different club - is a fantastic result for me."