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 (MLS) side Philadelphia Union, in 37C.
The 45% humidity means it feels more like 45C, according to accuweather.com, and temperatures on Monday were predicted to top 100 degrees Fahrenheit (37.8C) 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".
"It's been just about tomorrow's game, planning for tomorrow, and that's it. No more than that," the Italian added.
"As you can see, it's not easy in these conditions with these temperatures. We are going to try to do our best."