This morning Sydney coach Branko Culina admitted: "We don't know where he is - I am very disappointed."

Milligan was given time off from the club to recover from the rigours of the Asian Cup, but was expected to be back in training on Monday.

But Sydney have discovered Milligan flew out to Europe - and they have no idea when or if he will return.

Sydney don't even know which club he is trialling for, but believe it may be Lens or Metz. A brief article in French newspaper L'Equipe today confirmed Metz had been trialling the 21 year old Sydney FC player since Friday.

"The only thing we know is that he's gone overseas," said Culina today. "They don't need to behave like this. They don't have to do it in this sneaky way.

"There are procedures and protocols for this kind of thing. I don't blame Millsy, I blame his management.

"Good sensible people do not ignore the system or advice of others just so they can get their 10, 20 or 30 percent agent's fee. That's not going to help these players."

Milligan and Dave Carney have been linked with a range of clubs in Europe and the English Championship after their impressive performances for Australia in the Asian Cup.

But Sydney FC have not been contacted by any clubs and were hoping to be able to keep the players for the new season.

"We have rules about this sort of thing and I'm sure our CEO George Perry will be in touch with whatever club this turns out to be," added Culina.

"We have contracts in place to protect the club and players from just this sort of thing.

"But Milligan should not be jumping at opportunities like this. He and Dave are both in a position to pick and choose just about any club they like, except maybe something like Real Madrid or Barcelona.

"They shouldn't be dropping everything to sneak off and trial for a club like this. The clubs will have more respect for them if they play harder to get.

"And I speak as a man with vast experience as the father of Jason who has played for Ajax and PSV Eindhoven, which are both much bigger clubs than anything Mark will be trialling for."

He added: "We don't want to stand in the way of the players. If they want to go, we can help them.

"Obviously they would love the challenge to play overseas and they would dearly love to be part of the big picture.

"Despite what might be said by some, there's nothing we can do to match the money or allure of playing overseas - but Millsy doesn't have to take this kind of risk to play there."

Culina was already preparing for this weekend's pre-season match in Canberra without Milligan and Carney, but is now facing the prospect of losing him altogether.

And even if he does return to the club, Culina knows Milligan won't be in peak shape.

"We could have done as Ernie Merrick has with Archie Thompson who has gone with Victory to Darwin, and insisted Milligan and Carney both played," he said.

"But we thought we'd give them a rest and let them come back fully refreshed.

"Now though Mark will be flying 30 hours to Europe and 30 hours back again. It's going to be much harder for him."

He added: "If it was the off-season, this would be much less of a problem - but we are about to start our campaign.

"Our pre-season has been an absolute shamozzle because of our players being away on international duty or injured.

"But if a club now comes to us and says they want to take one of our players we will consider it.

"No-one has to be sneaky about it though."