Trace Cyrus says his dad Billy Ray Cyrus is ready to fight him in court … claiming his old man’s threatening legal action — while simultaneously begging him to seek treatment.

The adopted son of BRC posted to Instagram Saturday … claiming his recent social media post about his dad’s health came from a place of love — adding he could’ve blown the lid on a whole lot more about Billy but chose not to.

But, Trace claims his father didn’t take the message as one of love … claiming he’s now facing legal action from Billy — calling the move a “disgrace.”

And, Trace adds, he still loves his dad … but, he doesn’t respect him anymore.

TC ends with a strong message to his father … claiming everyone around him might be afraid to tell it as it is — but, he’s not. And, he thinks Billy needs to go get help.

As we told you … after Billy’s disastrous performance at a Donald Trump inauguration event, Trace said his dad wasn’t healthy and he needed to get help.

It’s caused a serious amount of Cyrus infighting this week … with Trace’s bro Braison working with Billy on an album — and Trace implied Braison is using drugs and alcohol too.