Brandon Marshall -- Johnny Manziel Is Sick ... He Needs Help

Brandon Marshall is calling for everyone to back off Johnny Manziel -- claiming he is suffering from an illness and needs help and support before it's too late.

The NY Jets wide receiver appeared on "Whitlock's House Party By the Bay" on FS1 Wednesday and said whatever Manziel is suffering from is a disease that needs to be treated.

Marshall says the pressures of the NFL can exacerbate issues -- and says he knows firsthand about what it's like to suffer from mental illness.

But the key, Brandon says, is Johnny needs to focus on treatment the same way he would prepare for an NFL game -- with 100% of his energy ... because that's what worked for him.