Tuchel was appointed Chelsea manager in January 2021, replacing club legend Frank Lampard in the role and he led the Blues to Champions League glory, beating Manchester City 1-0 in Portugal in May 2021.
The German tactician also led Chelsea to win the UEFA Super Cup and FIFA Club World Cup last year before losing the FA Cup and Carabao Cup finals to Liverpool last season.
Chelsea, under new owner Todd Boehly following Roman Abramovich's sanctions by the UK government, splashed the cash in this summer's transfer window, bringing in the likes of Raheem Sterling, Marc Cucurella, Kalidou Koulibaly, Wesley Fofana and Pierre-Emerick Aubameyang but they have made an indifferent start to the campaign.
Chelsea have won three and lost two of their six league games so far and the latest defeat to Zagreb has prompted the club's hierarchy to take action.
A club statement read: "On behalf of everyone at Chelsea FC, the club would like to place on record its gratitude to Thomas and his staff for all their efforts during their time with the club.
"Thomas will rightly have a place in Chelsea's history after winning the Champions League, the Super Cup and Club World Cup in his time here.
"As the new ownership group reaches 100 days since taking over the club, and as it continues its hard work to take the club forward, the new owners believe it is the right time to make this transition.
"Chelsea's coaching staff will take charge of the team for training and the preparation of our upcoming matches as the club moves swiftly to appoint a new head coach."
