"Kasey is a special case," Ziege said on the club's official Web site. "We've been friends since we played together at Tottenham, and that didn't make the situation any easier for me. Planning our goalkeeping situation was made more difficult because for a long time we didn't know if Keller saw a future for himself with Borussia in the Second Division.
"That he has now signaled his willingness to stay with the team was in fact a surprise. But we had to plan for the likelihood that if we were relagated he wouldn't be available and decided to make even the goalkeeping position part of out transition, and the age factor did play a role.
"Christofer Heimeroth will in the new season be our No. 1. He has our trust and that he has quality, which he displayed in the last few games [when Keller was injured]. Kasey Keller is not available as a backup goalkeeper, and that's why we'll acquire a second keeper. We want a man with some experience who is also dependable in case something happens."
Keller, 37, joined Gladbach midway through 2004-05 season, when his performances were hailed for helping the club stay in the top flight. Keller, who played in the top two tiers of the English league, and in the Spanish First Division, since moving to Europe in 1991, appeared in 78 Bundesliga games since joining the club. His contract with Gladbach expires in June.
Keller was at times during his stint with Gladbach rated among the Bunesliga's top goalkeepers and was a fan favorite.