Meteolux issued a yellow alert indicating a potential danger, adding on its website that the mercury was expected to reach between 30 and 32°C between 1pm and 7pm on Monday.
The warning comes a day after Luxembourg experienced record heat highs with the country. The temperature reached 31.5°C on Sunday, beating the previous record set on 25 May 2009 (30.4°C).
The weekend heatwave was thought to have been responsible for a fire in woodland between Kockelscheuer and Fentange on Sunday afternoon.
The heat is expected to ease off in Luxembourg during the week, with storms forecast for Tuesday.