Lampard appointed Chelsea head coach in July 2019 and finished in top four and reached FA Cup final last season; Chelsea ninth in Premier League after 19 games, 11 points behind leaders Manchester United.
In a statement, Chelsea said "results and performances have not met the club's expectations, leaving the club mid-table without any clear path to sustained improvement".
Tuchel, who left PSG in December and previously managed Borussia Dortmund, will be Chelsea's next head coach and plans are under way to appoint him before the game against Wolves on Wednesday. The German is the only candidate for the role.
Lampard, after being given more than £200m to spend on new players in the summer, Chelsea find themselves ninth in the Premier League after 19 games, 11 points behind leaders Manchester United and five points off Liverpool in fourth.
But after being given more than £200m to spend on new players in the summer, Chelsea find themselves ninth in the Premier League after 19 games, 11 points behind leaders Manchester United and five points off Liverpool in fourth.
In a statement, Abramovich said: "This was a very difficult decision for the club, not least because I have an excellent personal relationship with Frank and I have the utmost respect for him.
"He is a man of great integrity and has the highest of work ethics. However, under current circumstances we believe it is best to change managers.
"On behalf of everyone at the club, the board and personally, I would like to thank Frank for his work as head coach and wish him every success in the future. He is an important icon of this great club and his status here remains undiminished. He will always be warmly welcomed back at Stamford Bridge."
Souce: Sky Sports
