Gero moved to the Iran Professional League side Esteghlal from Ostersunds on a three-year contract in August after successful medicals but failed to meet the expectations.
The 24-year-old attacker replaced Mame Baba Thiam who scored 12 goals in 13 matches for Esteghlal but he has netted just one goal in nine matches for the Blues.
“The moment you stop challenging is the moment you stop moving forward. It has been an amazing experience playing in one of the best teams in Asia. Fun with everything since the first day I arrived here. I want also thanks my coaches, my teammates, and the club officials and also a big thanks to the lovely fans with their unbelievable heart support and once again thanks to everyone for my time I spent here in Iran and Esteghlal. Wish you all the best in the future,” Gero posted on his Instagram account.