KSI is taking on not one, but TWO challengers when he steps in the ring on Aug. 27 ... and his rival Jake Paul is crapping all over the idea -- saying the whole thing sounds like a setup.
The English YouTuber is slated to fight both rapper Swarmz AND Bulgarian pro middleweight Ivan Nikolov (3-16-2) at the O2 in London ... which is not the first time a boxer has had more than one opponent in a night.
In fact, George Foreman took FIVE fights in one day back in 1975 .