The 26-year-old has traveled to Tehran to undergo a medical examination.
Free agent Najdenov most recently played at the Egyptian club Smouha Sporting Club.
Cameroonian strikers Christian Bekamenga, Yves Ekwalla Herman, Portuguese forward Yazalde Gomes Pinto, Nigerian Salisu Abdullahi "Alhaji" Gero and had been already linked with Esteghlal.
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.