Caution

But Belgian coach Michel Bruyninckx, who works with the Aspire Academy in Qatar -- the gulf kingdom which will host the 2022 FIFA World Cup -- struck a note of caution.

"One of the major features of high performance is focused attention and that can be trained through this device," Bruyninckx told CNN.

"Brain research tells us that optimal learning requires that skill training must be embedded in the natural environment of an activity. This is not the case (with 'Footbonaut').

"The fact the player must react to a sound is not matching the reality of a game when a player reacts to visual information."

And the Belgian coach questioned the position of the player in the cage.

"The fact the performing player always stays in the central position is also a disadvantage. In a game he has to move and search for the best position to receive the ball.

"I am also curious to know how one-footed or technically less skilled players are going to react tn the 'Footbonaut'. For me you need to prepare a player for this kind of resource."

Bruyninckx also raised concerns over grueling physical workout which the cage gives a player.

"Using sweating as a parameter is not a good approach," he said. "Too often coaches think that high intensity delivers high performance. Brain research tells us that if energy is low, learning will go down."

So, while the "Footbonaut" is one small step for Dortmund, it could take a giant leap for the device to become a fixture at training grounds across the world.