Wada wanted the suspension to be increased to two years, but Guerrero also appealed in the hope it would be annulled.
The doping ban that will deprive Peru captain Paolo Guerrero of his long-awaited chance to play at the World Cup is unfair and defies common sense, the world players' union FIFPro said Tuesday.
The FPF said in a statement that it "profoundly regrets the lengthening of the ban imposed on our player Paolo Guerrero who has always shown exemplary conduct".
Guerrero was initially banned for 12 months after testing positive for cocaine metabolite benzoylecgonine following Peru'sWorld Cup qualifier with Argentina in October a year ago.
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.
Guerrero tested positive for cocaine following a World Cup qualifier in Argentina in October after drinking a tea containing the substance, CAS said.
But WADA effectively retaliated, appealing to CAS to uphold their original sanction.
Guerrero is Peru's record goalscorer and was named in their preliminary Russian Federation 2018 squad over the weekend, but his joy at being selected to represent his country at their first World Cup since 1982 proved short-lived.
Guerrero was serving a suspension when Peru beat New Zealand 2-0 over two legs in last November's intercontinental World Cup play-off.
Guerrero, whose lawyers argued that the Benzoylecgonine was accidentally consumed in tea, plays his club football for Brazilian outfit Flamengo.
"However, the panel considered that the player did bear some fault or negligence, even if it was not significant, and that he could have taken some measures to prevent him from committing the (doping violations)", the court said.
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.
It is the second ruling from sport's highest court that has weighed heavily on Peru's first World Cup appearance in 36 years.