Ten Hag joined the former Bundesliga champions this summer after being out of a job since November 2024, when the former Ajax boss was fired by Manchester United.
Bayer Leverkusen won three of their five games in preseason and started the official season off with a win over Grossaspach in the DFB Pokal, but got off to a bad start in the Bundesliga with a 2-1 home loss against Hoffenheim.
Speculation over Ten Hag's future in Germany arose over the past few days after Leverkusen conceded a 93rd-minute equaliser against Werder Bremen.
On Monday, the Werkself confirmed Ten Hag was relieved of his duties in West Germany.
"This decision was not an easy one for us. Nobody wanted to take this step," sporting director Simon Rolfes said in a club statement.
"However, the past few weeks have shown that building a new and successful team with this line-up is not feasible. We firmly believe in the quality of our team and will now do everything we can to take the next steps in our development with a new setup."
Club CEO Fernando Carro said the club would not have met their goals with Ten Hag in charge. "A separation at this early stage of the season is painful, but we felt it was necessary.
"Our goal remains to achieve the targets we set for the season – and to do that, we need the best possible conditions at all levels and across the entire first team. Now it's a matter of fully implementing and utilising these conditions again."
Assistants Andries Ulderink and Rogier Meijer will temporarily take over Ten Hag's first-team duties, the club confirmed.
Tasked with tricky rebuild
Soon after joining Bayer Leverkusen, the 55-year-old Ten Hag was tasked with filling the shoes of the illustrious Xabi Alonso, who won a famous domestic double with Bayer Leverkusen in the 2023/24 season and left for Real Madrid after the 2024/25 campaign.
The task soon became one of rebuilding the Werkself, as many key players had left during the transfer window.
Florian Wirtz and Jeremie Frimpong left for Premier League champions Liverpool, captain Granit Xhaka joined Sunderland, Amine Adli and Odilon Kossonou joined Bournemouth and Atalanta, and defensive anchor Jonathan Tah left for German giants Bayern Munich.
Leverkusen spent €173 million on replacements in the transfer market. Malik Tillman and Jarell Quansah joined for €35 million each, defender Loic Bade cost €25 million, and Mark Flekken was brought in for €11 million to replace Lukas Hradecky.
Return to Ajax on the books?
Ten Hag's near future is already the topic of discussion in his native Netherlands, where Ajax manager John Heitinga is under scrutiny for a poor start to the season.
After Francesco Farioli left the club earlier this year, Ten Hag was contacted by the Ajax board, but declined to negotiate a return to the Amsterdam giants.