The captains of the three teams facing Peru in Group C at the World Cup have signed a letter to FIFA urging world football's governing body to allow Peru captain Paolo Guerrero to play in the tournament.
FIFPro, which represents professional footballers, has written to world football's governing body asking for Guerrero to be allowed to represent his country.
France captain Hugo Lloris, Australia counterpart Mile Jedinak and Denmark's Simon Kjaer have all signed the letter.
Flamengo forward Guerrero was given a doping ban from the country's first World Cup for 36 years over cocaine contained in a cup of tea infused with coca leaves.
Earlier this month, the Court of Arbitration for Sport (CAS) upheld an appeal by the World Anti-Doping Agency (WADA) to increase the length of the ban.
Guerrero, 34, was initially banned for 12 months after testing positive for benzoylecgonine, a metabolite of cocaine, following Peru's World Cup qualifier against Argentina in October.
FIFA reduced the punishment to six months, which would have enabled him to play in Russia, and he was named in Peru's provisional squad.
But CAS increased it on the grounds that Guerrero bore "some fault or negligence" for the positive test and must face a ban of between one and two years under FIFA's anti-doping rules.
FIFPro has condemned Guerrero's ban as disproportionate and wrote on Twitter on Sunday that it hoped for "a breakthrough in the next 24-48 hours."