Canelo Alvarez and Gennady Golovkin
Gennady Golovkin is a "little upset" after Canelo Alvarez's failed drug test, says Abel Sanchez. Pictured: Alvarez (L) and Golovkin shake hands during a news conference at Microsoft Theater at L.A. Live to announce their upcoming rematch in Los Angeles, California, Feb. 27, 2018. Kevork Djansezian/Getty Images

Gennady Golovkin is said to be a "little upset" at Canelo Alvarez's failed drug test, according to the former's coach Abel Sanchez.

Golovkin is set to defend his World Boxing Association (WBA), World Boxing Council (WBC), International Boxing Federation (IBF), and International Boxing Organization (IBO) middleweight titles in a highly-anticipated rematch with Alvarez after their first encounter in September last year ended in a controversial split-decision draw.

While unlikely to happen, their fight on May 5 has a chance of being called off after Alvarez recently tested positive for clenbuterol, a banned substance commonly used by athletes as a fat-burner to help them cut weight.

After traces were found in his samples, Alvarez's promoters in Golden Boy Boxing defended him by claiming it was a case of contaminated meat consumed in Mexico, which has been a common occurrence in the past.

"I am an athlete who respects the sport and this surprises me and bothers me because it had never happened to me," Alvarez said in a statement. "I will submit to all the tests that require me to clarify this embarrassing situation and I trust that at the end the truth will prevail."

The Nevada Athletic Commission (NAC) is currently investigating Alvarez on whether his consumption of the substance was intentional but Sanchez claims Golovkin is disappointed that the Mexican's team was not more careful about the food he was consuming.

"He was a little upset also he was a little disappointed that his team wasn't more diligent about the food," Sanchez told Sky Sports. "But he knows that this is part of this game, and he just continues to train, and hopefully everything is alright, and we'll keep training until it's not."

Unbeaten "GGG" has been dominating the middleweight division for years and has knocked out 36 of the 38 opponents that he has faced. His stellar record and notorious power is one reason why Sanchez asked for drug tests so that no one could question Golovkin's credentials.

"About five years ago, I told [promoter] Tom [Loeffler] that there was going to be a point in time in Gennady's career where people would accuse us," Sanchez added. "I wanted to make sure that we volunteered for any kind of testing that they wanted. My gym volunteers for any kind of testing that they wanted."

"The first fight [vs Canelo] I think was a 45-day window. This time I wanted like a 90-day window, to make sure for the public that nothing is going on, and we get an even playing field."

Canelo Alvarez and Gennady Golovkin
Canelo Alvarez and Gennady Golovkin's first meeting ended in a draw. Pictured: Gennady Golovkin (R) reacts from an attack by Canelo Alvarez during their WBC, WBA and IBF middleweight championship fight at the T-Mobile Arena in Las Vegas, Nevada, Sept. 16, 2017. JOHN GURZINSKI/AFP/Getty Images

The new 90-day window has resulted in Alvarez's latest setback and while he does not want to speculate, Sanchez, who has had verbal back-and-forths with the 26-year-old of late, believes an investigation is crucial for the integrity of the sport.

"It would be ignorant for me to speculate," he explained. "I think the experts have to go through all the process of investigating, but I do think there needs to be an investigation."

"I don't think it should be just swept under the rug. That's not good for our sport. That's not good for the future of our sport. I think that he needs to either be cleared, or be suspended and fined immensely, but if he's not, then I think we present future problems for us in this game," he said.