Kusen general manager Reiner Calmund confirmed the decision, adding that Horster will be in charge for out trip to the Bay Arena on Tuesday.
"We regret the decision but given the precarious situation we were left with no other choice," he said.
"We have a very high opinion of him (Horster). He's a great tactician and a first-class coach. I don't want to rule out that he will also be on the bench next Saturday at Hanover."
Toppmoller’s side have struggled in the Bundesliga this season and only goal difference is keeping them out of the relegation zone, but even so the decision seems harsh.
Last season Toppmoller guided his side to the runners-up spots in the Bundesliga, German Cup and Champions League and then had to let both Ze Roberto and Michael Ballack leave the club in the summer.
Lets hope that we can make Kusen pay for their decision by registering home and away victories over them in the next two weeks.