Tsvetanov had been fired after Etar's 1-0 loss at Beroe Stara Zagora on 26 August, and then again a week later after the 1-0 home defeat by newcomers Pirin Gotse Delchev on September 1, only to be reinstated in both cases due to protest from fans.
The 42-year-old crowd favourite, capped 40 times and part of the Bulgaria team that finished fourth in the 1994 World Cup finals, was first appointed Etar coach in January and guided them to the top flight after 14 years in the lower divisions.
A club statement said Tsvetanov was fired for the third time in seven weeks due to a "series of statements against Turkish owner Feyzi Ilhanli and actions that undermine the prestige of the club".
Last month, Ilhanli accused Tsvetanov of being involved in match-fixing while Bulgaria's prosecutor has opened an investigation into suspicious games. Tsvetanov has denied any wrongdoing.
In happier times, Etar were 1991 Bulgarian champions and provided five players for the famous 1994 squad but are now second from bottom in a league characterised by bizarre stories.