The highly anticipated rematch between Canelo Álvarez and Gennady Golovkin is in jeopardy after the Nevada Athletic Commission filed a formal anti-doping complaint against Álvarez on Thursday in connection with a pair of failed drug tests last month.

Álvarez, a two-divsion world champion from Guadalajara, faces a ban of nine to 24 months at the hearing, which has been scheduled for 18 April. Even a reduced suspension would preclude Álvarez from participating in the 5 May blockbuster at the T-Mobile Arena, a sequel to last year’s controversial split draw at the same venue.

The fading possibility of the fight taking place as scheduled has prompted MGM Resorts International, which owns and operates the T-Mobile Arena, to start offering full refunds to ticket-holders at the original point of purchase.

Álvarez twice tested positive in random urine tests conducted by the Voluntary Anti-Doping Association on 17 and 20 February in Guadalajara, earning a temporary suspension from the commission. Golden Boy Promotions, which promotes the Mexican, have attributed the positive tests to contaminated meat, citing support from the laboratory that issued the tests – an alibi which Golovkin has openly mocked.

But the complaint filed on Thursday appears to invalidate that defense, saying: “Alvarez’s utilization, ingestion and/or consumption of Clenbuterol, whether intentional or not, constitutes an anti-doping violation.”

Clenbuterol, often used by asthmatics, has fat burning properties and athletes have been known to use it to help them drop body fat and weight quickly. Among those who have tested positive for it are four-division world champion Érik Morales, cyclist Alberto Contador and baseball players Raúl Mondesí and Guillermo Mota.

Álvarez and his legal team will explain their side of the story on 18 April to the five-member commission, which will decide the boxer’s fate by majority vote.