Monaco have announced the departure of Vadim Vasilyev as vice-president and general manager after six years at the club.
President Dimitry Rybolovlev praised the 53-year-old for his work in the Principality, but said a change was needed to end the "crisis" at Stade Louis II.
Under Vasilyev's guidance, Monaco became Ligue 1 champions and reached the semi-finals of the Champions League in 2016-17, but the loss of first-team stars such as Kylian Mbappe led to a decline that sees them lying 18th in the table after 24 games this season.
The club reappointed Leonardo Jardim as head coach last month, having sacked him in October and appointed Thierry Henry, who won just four of his 20 games in charge.
Vasilyev accepted full responsibility for "a very complicated time" at the club.
"Recently, I've been actively involved in managing and resolving the club's problems," Rybolovlev said in a statement on Thursday.
"I took a number of decisions that were difficult but necessary, in my opinion. In particular, I personally wanted to call Leonardo Jardim and apologise for the error made in October. I asked him to come back to the club to lead the team and I sanctioned all his proposals for the arrival of new players during the winter transfer window.
"It's time for a change. And these changes affect not only the workforce, but also the directors. So, I made a decision that is very hard for me, that of releasing Vadim Vasilyev as vice-president and general manager of the club.
"I am very grateful for all he has done for our club and wish him all the best for the future."
Rybolovlev, who plans to introduce a replacement on February 22, added: "This is not the first time Monaco has been going through a period of crisis. Seven years ago, we relieved the club from the very delicate situation in which it found itself.
"We strive again for such success. I am convinced these changes will allow us to achieve our goals."
Vasilyev said: "Despite the last few difficult months, I'm proud of the record at the end of these six intense years.
"I'm convinced the group is on the right track and that the end of the season will allow the players to show all their qualities to save this wonderful club."