"Ideally, Adelaide would be my number one choice but as you know in football, sometimes you have to move and I'd look forward to a new challenge. That could be a possibility. And Asia is a possibility as well," Costanzo told au.fourfourtwo.com.

"I'm a professional footballer. And there are other teams in the A-League who are playing in the [Asian] Champions League and two new clubs as well...but I'm just concentrating on the next couple of games."

After Adelaide's Club World Cup campaign, Costanzo, 32, will sit down with the club to assess where they are headed with their roster for season five of the A-League.

"If so, that's football, you move on and find another home," he added.

Adelaide have already brought in new defensive blood with Sydney FC defender Iain Fyfe returning to South Australia to ink a three-year deal this week.

"Fyfey has won championships so he brings that winning mentality with experience and he's going to be a handy acquisition.

"I'm pretty happy with the way I've been playing and the partnership with big Sasa has really been good. I'm feeling healthy, fit and raring to go.

"I've had some rest after the Central Coast game. The whole team was mentally drained but we've freshened up in the last two weeks."

One player definitely not staying is Jason Spagnuolo, who has negotiated an early release from his contract. The wide midfielder has struggled to get game time at Hindmarsh over the last year or so. Costanzo said it's disappointing.

"I was surprised and I'm disappointed." he said. "He's a fantastic guy and a fantastic player."

Around 10 United players are out of contract next year.

"Jason's here till the end of the season but like a number of us, we could be off as well... so we'll just have to wait and see."