The woman behind the thinly veiled threat goes by "Mia" -- she's the person who first published the bloody photos of Delicia Cordon on social media and blamed McCoy for the attack.

Initially, Mia spelled out her case against LeSean -- calling him a "devil" -- and accusing him of using steroids, attacking his own child, his dog and Delicia.

McCoy put out a statement adamantly denying Mia's allegations -- and a short time later, she deleted her post.

But Mia wants everyone to know she's NOT backing down -- and only pulled her post on the advice of Delicia's attorney.

She has now published a NEW post calling LeSean "Shady" McCoy a liar.

"For the record Delicia's lawyer forced me to remove that post. I stand by what I said," Mia wrote.

"I've personally addressed @leseanmccoy on everything that was stated many many times over the years. Lie to these people if you want Shady, but you know I know everything."