Dec 22 (Reuters) - Two-times Mexican national champion Luis Villalobos has been banned for four years after cycling"s governing body UCI said on Wednesday he had been found guilty of an anti-doping rule violation. UCI"s Anti-Doping Tribunal said it had found the presence of GHRP-6 -- a growth hormone-releasing hexapeptide and a prohibited substance on the World Anti-Doping Agency list -- in Villalobos" sample from 2019 when he was with U.S.-based Aevolo. "The Tribunal found the rider guilty of an anti-doping rule violation (presence of GHRP-6) and imposed a four-year period of ineligibility on the rider," UCI said in a statement. Villalobos, 23, had been provisionally suspended in May last year. He had joined EF Pro Cycling in 2019 but the team suspended the rider indefinitely after the adverse analytical finding. "If we"d have known, we would not have signed Luis. The burden of this is on the UCI because there is no internal testing program that has access to the level of equipment needed to screen for GHRP-6," the team"s CEO Jonathan Vaughters had said last year. Villalobos won the Mexican national time trial championship in 2018 and 2019.