The global footballers' union wants FIFA's help to review anti-doping rules after Guerrero was banned from the World Cup for a positive test for cocaine caused by contaminated tea.
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.
Guerrero, Peru's all-time top scorer, was suspended for a year by Federation Internationale de Football Association on December 8 after testing positive for cocaine metabolite benzoylecgonine following Peru's 0-0 draw away to Argentina the previous October, after apparently drinking tea containing the substance.
Guerrero was initially banned for 12 months, but that suspension was halved by Fifa's appeal committee.
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Guerrero was initially banned for 12 months after testing positive for cocaine metabolite benzoylecgonine following Peru's World Cup qualifier with Argentina in October a year ago.
It said in a statement: "The Cas panel confirmed the existence of an anti-doping rule violation (ADRV) committed by Mr Guerrero but also accepted that he did not attempt to enhance his performance by ingesting the prohibited substance".
The centre-forward has also previously represented Bayern Munich - scoring 13 times in 44 appearances for the German giants between 2004 and 2006 before leaving for Hamburger SV. 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. The substance is a metabolite of cocaine. Peru's captain and all-time leading scorer, Guerrero has become a lightning rod for Peru supporters, who showed up in masses to welcome him back to Lima after the CAS ruling was handed down. The first one was being awarded a default win over their opponents, Bolivia, who were found guilty of fielding an ineligible player.
Guerrero's appeal against the ban was upheld. It ended on May 3, making Guerrero eligible to play at the June 14-July 15 World Cup in Russian Federation.