Talking to the Sunday Post, Sadiq insists he was “humiliated” by being forbidden to train with the first team or even use the carpark at the club’s Hummel Training Centre.
The 22-year-old had a season-long loan from Roma cut short in January after failing to force his way into Gerrard’s plans.
He started just one match, a Betfred Cup semi-final where he imfamously blew a big chance in the 1-0 defeat by opting to dive as he tried to round Aberdeen goalkeeper Joe Lewis.
Now on loan at Serie B side Perugia, Sadiq claims he’s still owed his final payment before he left Scotland.
He said: “Once I put a ‘like’ on Instagram to a post from a fan – and I was fined £20,000, which was absurd.
“And Rangers didn’t even pay me up everything I was due. They still have to give me my salary for December.”
Sadiq also wasn’t impressed with how Gerrard communicated with him during his Rangers stay.
He said: “Gerrard proved to be very different from what I believed he would be.
“He phoned me three or four times, complimenting me and saying he’d back me to be a success. It made me feel important and convinced me to agree to the loan switch.
“But when I arrived, I didn’t even have any time to settle down before they brought in another striker, Kyle Lafferty.
“That was when the problems started, and my situation soon degenerated into a real nightmare.”
He added: “All of a sudden, I was told that I could not use the first-team dressing-room any more. Instead I had to go change with the kids.
“Then, after a few days, I was also forbidden to park my car inside the training centre. I felt humiliated and kept asking what was the reason for the change of attitude. But I never received any answers.
“Gerrard wouldn’t give any explanation about it, neither to me nor my representatives.”