The Peru international acted after being verbally abused by a Hamburg fan as he walked off the pitch.

He has already been fined an undisclosed amount by his club, but the DFB could dish out additional punishment.

A DFB statement today read: "The DFB have initiated an investigation against Paolo Guerrero.... Guerrero is suspected of a violent act against a spectator.

"Television pictures show him throwing a bottle into the stands and hitting a spectator in the face."

Guerrero apologised for his behaviour yesterday and admitted he had made a "big mistake".

"I had a blackout," Guerrero said on www.hsv.de. ``I was insulted and I over-reacted.

``I am incredibly sorry. I hope that I get the opportunity to apologise personally to the spectator concerned.

``I have already done so to HSV. Of course I will accept any punishment from the club. I made a big mistake.''