The Polish Weightlifting Federation says that it has received information from the Commission Against Doping in Sport that Adrian Zielinski, who won a gold medal at the London Olympics in 2012, has tested positive for a performance-enhancement substance, nandrolone.
The federation said on its website on Friday that the sample was taken from Zielinski on July 1 during a competition in Poland.
Polish media are reporting that Zielinski will not be allowed to compete at Rio and that he is preparing to return to Poland.
He is quoted as denying having taken banned substances and said he has no idea how the substance could have been found in his body.
The Polish Weightlifting Federation says he has a legal right to a B sample.
Earlier in the week Zielinski's brother Tomasz, also a weightlifter, was also sent home from Rio after testing positive for nandrolone, a steroid.