Floyd Mayweather's Uncle, Roger Mayweather -- one of the most famous boxing trainers in the world -- has gone missing ... and family members are concerned, saying he needs his medication as soon as possible.
Roger was also a pretty good boxer ... and battled with some pretty big starts, including Julio Cesar Chavez and Ray "Boom Boom" Mancini.
The LVMPD has issued an official missing persons alert ... saying Roger was last seen Saturday afternoon near the Mayweather Boxing Club in Las Vegas.
He's 5'7" and 160 lbs.