One of the world's best featherweight fighters will be out until 2018.

Chad Mendes has been suspended for two years by USADA after testing positive for a performance-enhancing drug in an out-of-competition sample May 17, the UFC's anti-doping partner announced Wednesday. The banned substance GHRP-6, also known as growth-hormone releasing hexapeptide, was found in Mendes' system.

Mendes, 31, won't be able to return to the UFC until June 10, 2018, two years from the date of the beginning of his provisional suspension. When reached by MMA Fighting, Mendes declined comment Wednesday.

Mendes (17-4) has been one of the UFC's best 145-pound fighters for the last five years. The Team Alpha Male product is coming off a knockout loss to Frankie Edgar in December. Mendes challenged former featherweight champion Jose Aldo in title fights on two occasions.

The California native owns victories over the likes of Ricardo Lamas, Clay Guida and Cub Swanson. In his most high-profile fight, he fell to Conor McGregor via second-round TKO in the main event of UFC 189 with the UFC's interim featherweight title on the line.