The 'Lucifer' heatwave which is hitting central Europe has caused temperatures to rise towards 40 degrees, the temperature which is forecast for Tuesday evening when Real Madrid and Manchester United meet in Skopje.
If the sweltering heat poses a threat to player safety, that is if it exceeds 32 degrees Celsius, UEFA will implement a three-minute water break every 30 minutes to keep players hydrated.
When the two sides faced each other In Santa Clara a fortnight ago the players enjoyed these water breaks, which will be decided in Skopje by a match delegate who will monitor conditions and have the final say.