In anticipation of the Monday Night Football special set to take place on November 21 in Mexico City between the Oakland Raiders and the Houston Texans, the NFL has put out a warning to all players: do not eat meat in Mexico.

Apparently, clenbuterol – a supplement used by cattle farmers to make cows meatier – has been found in meat produced in Mexico and China. (Cue an excuse for every failed drug test we come across for the foreseeable future). The substance is banned in Mexico, the U.S., and by the NFL Policy on Performance Enhancing Substances.

An early morning memo from the league read that “there is evidence that some meat produced in China and Mexico may be contaminated with clenbuterol, an anabolic agent which is banned by the NFL Policy on Performance-Enhancing Substances. Consuming large quantities of meat while visiting those particular countries may result in a positive test for clenbuterol in violation of the policy.”

CONMEBOL put out a similar warning to its soccer stars a few months back, alerting athletes to the potential for testing positive for clenbuterol and failing drug tests should they choose to eat meat in Mexico.

In 2011, five players on Mexico’s national soccer team tested positive for the substance, and over 100 players were said to have tested positive during the U-17 World Cup held in the country from June to July of the same year as well.