David Wagner was sacked by Schalke two matches into the Bundesliga season.
Schalke lost 8-0 in their opening match against Bayern Munich, and lost 3-1 to Werder Bremen over this weekend.
Schalke have not won in 18 Bundesliga matches.
"We had all hoped that we could improve on the pitch together with David Wagner. Unfortunately, we haven't seen the right performances and results from the first two games of the season for this to happen," said Jochen Schneider, Schalke's sporting director.
"We have therefore decided to make a fresh start. Despite the disappointing results, this wasn't an easy decision for us to make."