The player who's ranked No.77 in the world said that he did not knowingly take a banned substance and that the news was "the biggest shock."
Majchrzak, who won the Challenger Tour event in Busan, South Korea in October and reached the semi-finals of an ATP 250 event in Pune, India earlier this year, did not provide further details about the banned substance.
The ITIA said on Friday that Majchrzak had provided samples from tournaments at Sofia in September and Japan and Seoul in October which were found to contain three banned substances (SARM S-22, LGD-4033 and PPARδ agonists).
"I have some incredibly sad and difficult news to share with everyone. I have tested positive in anti-doping controls during October and November 2022," Majchrzak wrote in a post on Instagram.
"Firstly, I have never, ever, knowingly taken any banned substance. At this moment I have no idea what has happened and this is the biggest shock.
"I have started the most difficult fight of my life -- the fight to prove my innocence and to return to the sport I love."
The ITIA said the player can request that his B samples are analysed to see if they confirm the A sample findings.
"While provisionally suspended, he is ineligible to compete in or attend any sanctioned tennis events organised by the governing bodies of the sport," the ITIA said.
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