Temperatures in Macedonia’s capital of Skopje have hit 40C, with the heat still set to be around the 32C mark by kick-off at 7.45pm (8:45pm local time) on Tuesday.
UEFA have made provisions for two water breaks, in the 30th and 75th minutes, should the temperature exceed 32C by the time the game gets under way.
United and Real were allowed similar water breaks when they met in Santa Clara last month on their pre-season tours of the US, where Jose Mourinho’s side won on penalties after the two sides drew 1-1.
lt is likely to be the hottest they have endured.
The energy-sapping test in the debilitating against heat comes just five days before Mourinho’s United begin their Premier League campaign against West Ham at Old Trafford.
Health warnings are in place in the parts of Southern Europe where temperatures – the highest recorded for a decade in some regions – have reached potentially dangerous levels.