Milligan was left on the deck for several minutes and limped from training in Antalya, Turkey, on Saturday after sustaining the injury.

He was attended to do by Socceroos medical staff and appeared to be in some distress.

It is unclear yet about the severity of the injury, which will likely require scans.

Ex-Socceroo Mark Schwarzer was watching training for Optus Sport and said: "It's one of those where it looks like he felt something, a bit of a tweak.

"He went down, got a bit of hands-on treatment. Got up, shook his legs around a bit and if it was really serious he wouldn't be doing that.

"I'm more confident it's maybe a tight tweak."

Socceroos boss Bert van Marwijk will need to trim three players from the training squad for the final 23-man World Cup squad.

Milligan, who plays in Saudi Arabia was Al Ahli, has been a mainstay in the Socceroos team in recent years.

He's also been to three World Cups before with the Socceroos in 2006, 2010 and 2014.

"He's an important player to the squad," Schwarzer said.

"He's got vast amounts of experience ocnsidering we don't have a lot in the squad.

"If he was to miss out because of it, it'd be a bit of a disaster for us."