Peru's hopes of making the World Cup finals suffered a potential setback on Friday when it was reported Brazil-based striker Paolo Guerrero had returned an "abnormal result" from a post-match drugs test.

Media reports in Peru and Brazil, where 33-year-old Guerrero plays club football for Flamengo, claimed that the test took place after a World Cup 0-0 qualifying draw against Argentina on October 5.

Peru are due to face New Zealand over two legs in an inter-continental qualifier later this month with the winner booking a place in the 2018 finals in Russia.

"What exists now is an abnormal test for a stimulant substance and in this case it is not considered a positive result," Fernando Solera, the head of the anti-doping committee at the Brazilian football federation, told SportTV.

"For the moment, Guerrero is not considered as doped."

"We cannot talk about the substance in question -- the player has the right to defend himself and demonstrate what this substance is," Solera added to ESPN Brazil.

Peru will face New Zealand over two legs on November 11 and 15.