Jose Canseco is REALLY pissed at Logan Paul over the breakup with his daughter -- suggesting something scandalous went down behind the scenes.
The ex-MLB star isn't spilling all of the tea ... but says the split between Logan and supermodel Josie Canseco earlier this year "left me with a bit of a bad taste in my mouth."
Now, 56-year-old Jose wants to FIGHT the 25-year-old YouTube star defend his family's honor.
... and yeah, Jose insists this is for real.