Kownacki, who just five years ago boasted a perfect 20-0 record and was touted as a potential opponent for the likes of Anthony Joshua, endured what could be his final professional career outing.
The Polish heavyweight lasted just 45 seconds in the first round as Meyna connected with a number of big shots before the referee stepped in to stop the bout.
This is the fifth straight defeat for Kownacki, with the 34-year-old previously losing to Joe Cusumano, Ali Eren Demirezen and twice to Robert Helenius.
Just a few years ago, the Pole was seen by many as a serious contender as he picked up victories over former world title holders Charles Martin and Chris Arreola.
Any hopes of a championship opportunity were dashed by his continuing losing run.
More concerning than the defeats themselves is the manner in which Kownacki has suffered them.