According to the depor.com, Farfan collided with a teammate and lost consciousness during the training session on Saturday.
The 33-year-old forward has undergone medical tests in Moscow and stayed at the hospital as a precaution.
Peru lost 1-0 to France in their second Group C match on Thursday, while also suffering defeat in their first game against Denmark by the same scoreline.
Jefferson Farfán sufrió un golpe en la cabeza en el entrenamiento de hoy, quedó inconsciente y fue traslado a una clínica, ojalá que no sea grave 🙏 pic.twitter.com/FqAxt0Ubqy— Guerreros Peruanos (@PeruanosInfo) June 23, 2018
Peru’s defeats mean they have been eliminated from the World Cup and have yet to score a goal at the tournament.
The 2018 FIFA World Cup in Russia kicked off on June 14 and will continue until July 15, with the matches being played in 11 cities across the country.