Shakur Stevenson says it'd be a baaad mistake for Vasyl Lomachenko to step in the boxing ring with him ... telling TMZ Sports he'll straight up whoop his ass!!
23-year-old Stevenson -- one of the most talented, young boxers in the world -- is fighting Toka Kahn Clary Saturday night (more on that later) ... a fight Shakur says is a warm-up for Loma.
Of course, 32-year-old Loma lost to 23-year-old Teofimo Lopez -- a big-time upset -- in October ... but is still considered one of the best pound-for-pound boxers in the world.