Monaco, languishing 18th in Ligue 1, said Thursday that they have sacked Leonardo Jardim, who led them to a French title in 2017.
Monaco wished Jardim, who also led the club to a Champions League semi-final in 2017, and his staff "the best for the future."
The club from the principality would not comment on a replacement, but their former player Thierry Henry has been linked to the job.
Henry was youth player with the club and scored seven goals in the 1997-8 Champions League as another talented Monaco team, this one coached by Arsene Wenger, reached the semi-finals, where they lost to Juventus.
He was then sold to the Turin club and went on to a successful spell with Arsenal in England and World Cup and Euro-2000 winners medals with France.
Henry is an assistant coach with Belgium, which finished third in the summer's World Cup.
He has recently been linked with jobs at Aston Villa and Bordeaux, but in both cases negotiations broke down after initial meetings.
Jardim was at Monaco since 2014 and was under contract until 2020.
The 44-year-old Portuguese coach had to cope with the sale of many of the stars of his title-winning squad over the last two seasons.
This summer Thomas Lemar, Joao Moutinho and Fabinho followed earlier departures Kylian Mbappe, Benjamin Mendy, Bernardo Silva, Tiemoue Bakayoko and Valere Germain out of the club in lucrative transfers.
Monaco lost their last game 1-0 at home to humble Angers and have not won in Ligue 1 since their opening match and have lost both their Champions League group games.
Against Angers, the only key members of the title-winning team to feature were skipper Radamel Falcao and the defensive trio of Jemerson, Kamil Glik and Djibril Sidibe.
Meanwhile, a summer spending spree headed by the signing of Russian World Cup star Aleksandr Golovin has not yet produced positive results for a club owned by Russian billionaire Dmitry Rybolovlev.
"I would like to salute Leonardo with the utmost respect for all the work done," AS Monaco Vice-President Vadim Vasilyev said in a statement.
"His brief time will remain as one of the most beautiful pages in the history of the club. Leonardo will always be part of the family of AS Monaco."
Monaco's next match, after the international break, is on October 20 away to Strasbourg in Ligue 1.