As if things couldn't get any worse for Michael Porter Jr.'s family -- the Denver Nuggets star's brother, Jevon, was arrested on suspicion of DWI late Friday night ... just days after his sibling, Coban, was sentenced to six years in prison in his fatal DUI case.
TMZ Sports has confirmed .... Jevon -- who recently transferred to LMU after previously playing at Pepperdine -- was initially pulled over around 1:30 AM in Missouri for speeding prior to getting busted for DWI.
Officials are still investigating the incident .