Former European Footballer of the Year Stoichkov, 47, also said referee Georgi Yordanov had "made fun" of his players by showing them cards and not awarding them a penalty in Wednesday's Bulgarian league match.
Stoichkov also received a one-match touchline ban for "insulting officials in the media", the BFU's disciplinary commission said in a statement.
Stoichkov, who as a player had frequent arguments with referees, told local media: "I just don't care about the fines."
After Wednesday's profanity-laden verbal attack on Mihaylov, Stoichkov had told reporters: "I'll catch him somewhere and I'll beat him up. This will happen."
The Dagger, as Stoichkov is known in the Balkan country, was part of the team alongside former keeper Mihaylov who led Bulgaria to the 1994 World Cup semi-finals in the United States.
He was also a key member of Barcelona's "Dream Team" coached by Johan Cruyff.
Litex are fifth in the standings with 49 points with one game remaining. Relegation-threatened Lokomotiv are 13th on 28, two points from safety.