CSKA Sofia coach Stamen Belchev resigned after about a year and a half in charge, having failed to outclass Ludogorets in the Bulgarian league title race or win any other trophy.
"After a series of negative results, Stamen Belchev decided to quit his post as head coach," CSKA, still the most successful club in the Balkan nation with 31 league titles, said in a statement.
The 48-year-old had been seeking to end Ludogorets’ domination of the domestic league in recent years. CSKA had looked like title contenders in the first half of the season but the team`s performance was criticised in recent months.
Ludogorets clinched their seventh successive league title with four games to spare on Sunday.
CSKA, one of the two most popular Bulgarian clubs alongside city rivals Levski Sofia, have not won the domestic title since 2008.
The Reds, as CSKA are known in Bulgaria, named Hristo Yanev as their coach for the remainder of the season, the club said.
Yanev, a former midfielder and national team player, coached CSKA for about a year until August 2016 during a period when the club was demoted to the third division due to a financial crisis. He made history when CSKA become the first third-tier club to win the Bulgarian cup.
CSKA, founded in 1948 as an army club, mark their 70th anniversary on Saturday when they host Ludogorets at the Vasil Levski national stadium, expected to be one of the best attended matches in the domestic fixture.