Monaco stretched their winless Ligue 1 start to two games after a first-half penalty from Terem Moffi gave Lorient a 1-0 win over the principality side on Friday.
Moffi converted the 31st-minute spot kick after he was hauled down by Ismail Jakobs shortly after Sofiane Diop skied his shot over bar from a good position at the other end.
Monaco had 72 percent of the possession in the first half but Lorient came close to doubling their lead when left back Vincent Le Goff shaved the top of the bar with a cross-turned shot in the 43rd minute.
Defender Strahinja Pavlovic glanced a header inches wide for the visitors shortly after the break but that was as close as they came to an equaliser as they created little up front against a packed Lorient defence.
In Saturday's standout fixture, Paris Saint Germain are at home to Strasbourg with new signing Lionel Messi to be presented to the fans before the kickoff.
(Writing by Zoran Milosavljevic; Editing by Pritha Sarkar)