Chelsea manager Enzo Maresca says it is "impossible" to organise normal training sessions amid a "code red" severe heat warning in Philadelphia at the Club World Cup.
The Blues players trained at Subaru Park, the home of local Major League soccer side Philadelphia Union, in 37C heat.
The 45 percent humidity means it feels more like 45C, according to accuweather.com and temperatures on Monday were predicted to to reach over 100C Fahrenheit (37.78C) for the first time in 13 years.
"This morning's session has been very, very, very short," said Maresca, adding that "otherwise you don't save energy for the game".