Chelsea midfielder Enzo Fernandez said he has felt "dizzy" while playing in "very dangerous" heat at the Club World Cup in the United States.
The 24-year-old has featured in all six of Chelsea's matches en route to the final against Paris St-Germain in New Jersey on Sunday.
Three of Chelsea's games were played in temperatures described as "extreme heat", with local weather warnings urging people against involvement in strenuous physical activity or being outside.
In New Jersey, where Sunday's final takes place, temperatures have reached 38C in recent days.
Manager Enzo Maresca has complained it is "impossible" to have a normal training session because of the heat, despite reaching the final of the lucrative and newly-expanded tournament.