The 26-year-old player has signed an 18-month contract with the Blues.
The details of the Najdenov’s contract have not been revealed.
Free agent Najdenov most recently played at the Egyptian club Smouha Sporting Club.
The Blues need to strengthen their team for the 2018 AFC Champions League.
Esteghlal has been drawn along with Al Rayyan of Qatar, Al Hilal of Saudi Arabia and Al Ain of the UAE in Group D of the competition.
Esteghlal will meet Al Rayyan of Qatar on Feb. 13 in Doha in its opening match.
Winfried Schafer’s team also sits sixth in Iran Professional League, 19 points behind pacesetter Persepolis.