The French club sneaked Milligan out of Australia to trial for them last week, but the move was only arranged at the last moment after two key players were injured on Wednesday.

Julian Cardy and Sebastien Bassong were both ruled out of action for up to two months, plunging Metz’s defence into crisis just a week out from the start of their Ligue 1 season.

"The injuries are inevitable during a season,” admitted Metz coach Francis De Taddeo. “Only this time, it is a matter of two important elements of the team injuring themselves simultaneously and for an identical length of time.

“That did not happen to us last season. This is a hard blow.”

The club brought in Milligan to trial for them as potential cover for the two players. Despite reports to the contrary, he was not originally being lined up to take part in the club’s friendly against Belgian side Standard Liege.

The club added: “To compensate for their absence, the club has moved to reinforce.

“International Australian Mark Milligan will stay some days so the technical staff can observe him, but will not be tested against Standard Liege.”

However De Taddeo changed his mind just before kick-off and said Milligan could be brought on, despite suffering jetlag after his 30 hour flight to France.

But instead Milligan was not even named on the bench for the tie, sparking speculation he had walked out on the French club.

The discovery that Milligan was only wanted as back-up for the Metz defence will add insult to injury for Sydney – and will be a crushing disappointment to Milligan himself.

He would have been keen to have a guaranteed first team place after his heroics in central defence for the Socceroos at the Asian Cup.

And he would not want to be playing second fiddle to more established stars currently on the injury list.

He risked his future at Sydney FC by vanishing from Australia last week to fly to Europe for the trial with the French club, infuriating Sydney coach Branko Culina.

He admitted at the weekend: "We don't know where he is - I am very disappointed.

"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.”

Metz have yet to comment on reports Milligan has now walked out on the trial and was heading for a meeting with his agent in London over the debacle.

However the French club this morning announced they have now moved to fill the gap in defence. They signed veteran former Metz defender Jeff Strasser, 32, for two years on a free transfer from Racing Strasbourg to ease the defensive crisis.

Last night Sydney FC said Milligan was now expected back at the club on Wednesday when they would make a decision on any disciplinary action.

"We're very disappointed with what's happened," CEO George Perry told the Sydney Morning Herald.

But he revealed the club did have some prior warning of Milligan's exit from the club, despite Culina apparently being kept in the dark about it.

"It wasn't until the day before he [Milligan] left that we knew anything about it, and as of today we still haven't had anything official from Metz," he said.

"Mark has been told he's required to be back for training on Wednesday, and we expect him to be here."

He added: "As for any punishment, well, that's being discussed, and whether it's against him or his agent [Craig Nettelbeck] remains to be seen.

"If people decide to take matters into their own hands, it's fair to say there may be consequences.

"When a player is under contract, it comes with certain responsibilities."