Levski seemed certain to win a 27th league title on Saturday but, in a dramatic finale, defender Dimitar Vezalov scored a bizarre own goal 16 minutes from time while rivals Ludogorets beat Montana to lift the trophy for a second straight year.
"One of our players was crying in the dressing room after Levski failed to win the title," Stefanov told a news conference. "No doubt, he will not be part of Slavia anymore."
Stefanov gave a strong hint he was talking about midfielder Dimo Atanasov when revealing the player was a product of local club Pavlikeni's youth academy and reportedly a Levski fan.
The 27-year-old, who has also played for Lokomotiv Sofia, Botev Plovdiv, Lokomotiv Plovdiv and champions Ludogorets in the top flight, was an unused substitute in Saturday's draw.
Slavia, who mark their 100th anniversary this year, assigned bodyguards to goalkeeper Georgi Petkov and coach Velislav Vutsov after they got death threats following the oldest Sofia derby.
Petkov, formerly with Levski, made an outstanding save in the last minute, depriving the home team of their first title since 2009, while Vutsov was Levski coach in 2009.
The pair were called "traitors" by the Levski supporters.
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