The Spanish cyclist, who rode for Burgos-BH, was sanctioned in October 2018 after six blood samples from the previous year showed abnormalities.
However, at the start of 2019, the Administrative Court of Sport of Spain lifted the ban, saying that no infringement had been proved.
Salas leads the pack
Image credit: Getty Images
In response, the World Anti-Doping Authority lodged a case with the Court of Arbitration for Sport, who have upheld the first decision.
All his results back to January 2017 are now nullified and he will not be able to ride again until January 2021.
In a statement, CAS said that Salas Zorrozua's biological passport had "highly abnormal" values "and indicated a high probability of doping".