The Greco-Roman wrestler tested positive in June 2014 for the banned anabolic steroid, Trenbolone, during the Greco-Roman World Cup in the Iranian capital Tehran on May 16.
He was handed a two-year ban for doping.
“I think it’s time to go and I wish all the best for the Iranian wrestlers at the Rio Olympic Games,” Nematpour said in a message.
Nematpour won gold in the Greco-Roman 84 kilogram category at the 2013 World Championships in Budapest, Hungary.
He had also won a gold medal in the 2010 Asian Games in Guangzhou, China.