Spanish anti-doping authorities are investigating a possible violation by Denis Cheryshev.
During the World Cup, Cheryshev's father gave an interview in which he said that his son had been given an injection to treat an injury prior to the tournament. That injection, he was quoted as saying, contained a growth hormone. He later claimed that he had been misquoted. The player also denied taking HGH.
Cheryshev plays his club football for Valencia, where he is currently on loan from parent club Villareal.
"We can confirm we have started an investigation to find out more information about the case," said a spokesperson for AEPSAD.
"The investigation is being carried out with the co-operation of Russia’s anti-doping agency and is in contact with the World Anti-Doping Agency."
The 27-year-old scored four goals at the World Cup, two were nominated for Goal of the Tournament.
The taking of HGH without permission carries a possible four-year ban.
"On my side, everything has been honest and I think there will be no problem," the player told Russian paper Sport-Express.
"I think we'd better leave this case in the hands of medics, who have done everything right."