Motahari was a key member of Zob Ahan football team in the AFC Champions League group stage, helping the Iranian team book a place in the knockout stage.
Iranian media reports suggest that Motahari has reached an agreement with the popular football team.
Esteghlal has yet to confirm the transfer because the team has not named its new head coach so far.
The 26-year-old forward started his playing career at Naft Tehran in 2014 and has also played in Iranian top-flight football teams Pars Jonoubi and Tractor Sazi.