The 33-year-old quit his Croatian team Dinamo Zagreb earlier this month because of the knee problem.

"This latest injury was the final straw," Nowotny told Kicker magazine. "Of course on a physical level I have suffered worse injuries, but the thought of spending another extended period on the sidelines, another recovery and another return to training, that's too much."

The former Bayer Leverkusen captain played in the German team that finished third at last year's World Cup.

Nowotny spent 10 years at Leverkusen, where he arrived from Karlsruhe, before joining Dinamo after the World Cup.

He signed a three-year deal and played 12 matches but injured his knee in August.

He went under the surgeon's knife in Zagreb but that failed to cure the problem. He had another operation in Germany but in mid January he and the club agreed to part their ways.

Nowotny played 334 games in the German Bundesliga, scoring 11 goals, and played 48 times for the national side, scoring once.

Nowotny was a last minute call-up to Jurgen Klinsmann's World Cup squad last year, having missed the 2002 version through injury.

He suffered that during the Champions League semi-final second leg against Manchester United that year and missed the end of Leverkusen's 'nightmare' 2002 season in which they finished runners up in the league, Cup and Champions League.