Paul Pogba's backup B sample has also tested positive for testosterone, meaning the Juventus midfielder now faces a doping investigation.
The exams were carried out by Nado Italia, Italy's anti-doping agency, which suspended Pogba provisionally nearly a month ago following a positive test carried out after Juventus' game at Udinese on Aug. 20. Pogba did not play in the Serie A match but was on Juve's bench.
Pogba remains suspended provisionally and risks a ban of up to four years.
Neither Pogba nor Juventus has publicly contested the results of the tests.