"He'll be out for four to five weeks," coach Ottmar Hitzfeld told reporters in Munich. "The operation will be done as soon as possible."

The 38-year-old keeper aggravated his elbow injury, which haunted him over the past months, while warming up before Bayer Leverkusen's game.

He was replaced by Michael Rensing who is seen as his future successor.

Kahn will miss Belenenses tie in the UEFA Cup clash and Bundesliga games against Nurenberg, Bochum, Dortmund and Frankfurt.