Bayer Leverkusen goalkeeper Fabian Giefer says he has no memory of the crucial mistake that led to a goal in his side's 2-0 defeat by Mainz in the Bundesliga on Sunday - nor of the game itself.

The 21-year-old suffered concussion after colliding with Mainz forward Eric Maxim Choupo-Moting's knee in the 84th minute of the game. He played on, but was kept overnight in a Mainz clinic for observation.

Giefer told the Express newspaper Tuesday: ''I have a complete blackout. I didn't even know how we played. I also know nothing of my mistake. Neither can I remember our preparation for the game, the hotel in Mainz, nor even our training camp.''

Giefer mis-hit a simple pass across the face of goal to allow Sami Allagui to open the scoring in the 32nd.