The former Ajax and Manchester United manager lasted just three games before Bayer's board decided to part with the Dutchman.
BILD says before the decision, the relationship between Ten Hag and staff had become increasingly strained, while there were claims the players were left in the dark over the coach's tactics and demands.
Ten Hag, who had succeeded Xabi Alonso, saw the team dismantled over the summer as Florian Wirtz, Jonathan Tah, Jeremie Frimpong, Piero Hincapie and Granit Xhaka.
It's suggested long-serving Bayer staff would debate whether Ten Hag was the "worst" coach the club had hired.
Explaining the decision, Bayer chief Simon Rolfes said: "From the impressions from preseason, from the first games, we had the feeling that we had to do it now.
"You can make bad decisions, but if you then believe you've reached the point where it can't work in the future, it's an even bigger mistake to let it continue."