Taking into account the circumstances of the case, the FIFA AC imposed a 6-month period of ineligibility on the Player, instead of the 1-year minimum suspension provided by the FIFA Anti-Doping Regulations, applicable in case of no significant fault or negligence.
But CAS have increased Guerrero's suspension from six to 14 months on the basis that he did bear "some fault or negligence" for the positive test, and must therefore face a ban of between one and two years under FIFA's own anti-doping rules.
Paolo Guerrero is out, and if that's an unfamiliar name, you're obviously not Peruvian.
FIFPro says a 14-month ban barring the 34-year-old Guerrero from his World Cup debut is 'unfair and disproportionate'.
"Both FIFA and the Court of Arbitration for Sport agreed Guerrero did not knowingly ingest the substance and that there was no performance-enhancing effect".
The CAS made a decision to increase Mr Guerrero's suspension from 6 to 14 months, starting today, with the period of provisional suspension of 6 months already served by Mr Guerrero being credited against the total period of ineligibility to be served. They questioned the CAS's intentions for the ban despite admitting that Guerrero was not significantly negligent and his intention was not to enhance his performance.
The news comes as a blow to the Peruvian national team, who are set to play in their first FIFA World Cup since 1982, who had named Guerrero in their provisional squad just yesterday.
Accepting Guerrero's argument that the substance was accidentally consumed in contaminated tea, Federation Internationale de Football Association reduced the ban to six months, a period which would have enabled Guerrero to play in Russia, and he was duly named in Peru's provisional squad on Sunday.
It is the second ruling from sport's highest court that has weighed heavily on Peru's first World Cup appearance in 36 years.
Guerrero, who is Peru's all-time record scorer with 32 goals, played for Brazilian side Flamengo last week on May 6 at the conclusion of his six-month ban.