"It was a positive test and it seems to be very difficult that the fight scheduled for November 4 could take place," WBC spokesman Victor Cota told AFP.
However, the bout has not been cancelled as the test was carried out by the Voluntary Anti-Doping Association (VADA) and is therefore not official.
"He has the possibility to do another test," added Cota.
On Thursday, WBC president Mauricio Sulaiman announced on Twitter that his organisation had "received confirmation from VADA of a positive test by Luis Ortiz".
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