The Manchester City defender returned to England today for further tests after spending yesterday afternoon in hospital undergoing tests on a knee injury.

Boateng had been set to replace the released Philipp Lahm at left-back but that job will now be fulfilled by Marcel Schmelzer.

Assistant coach Hans-Dieter Flick today confirmed Schmelzer, Mats Hummels and Christian Trasch will start in an experimental side which will also see Mainz forward Andre Schurrle start his first international.

"We have several options and will have to see what we decide to do," said Flick, who has not ruled out a change from the usual 4-2-3-1 system.

"An alteration is possible but we have yet to decide that. We have a lot of strength in depth in our squad and every player has got to be able to stand in for anybody else, whether they play in the same club or not."

Borussia Dortmund defender Schmelzer is looking forward to his debut at the Borussia Park Stadion.

"I am delighted to be here," he said. "This is a good chance for us young lads to show what we can do and put the pressure on the elder players.

"We are all good footballers and all play for good clubs in the Bundesliga.

"This game against Australia is a chance for me to show the coach what I can do."

Schmelzer will come up against one of his team-mates tomorrow night with Mitch Langerak expected to start in goal for Australia.

"We are delighted that Mitch is part of the Australia team, but there is no betting as to how many goals we will put past him," added Schmelzer.

"Mitch is a really good, young goalkeeper and especially we younger players spend a lot of our free time together.

"I think he has a great future ahead of him."

Injury has forced Australia coach Holger Osieck to leave Tim Cahill out of his squad for tomorrow's friendly.

The Everton midfielder is still recovering from a foot injury and Osieck decided not to risk him.

But the Socceroos coach is nevertheless bullish about his side's chances, telling Kicker magazine: "We want to not only match Germany, but also entertain the fans. It is a prestigious match."