The 24-year-old was not included in the squad for the trip to Craven Cottage but trained in Manchester on Saturday.
Mendy was reprimanded by Pep Guardiola last September after he attended an Anthony Joshua fight in London and was late for training the next morning.
Guardiola was more relaxed when he learned of Mendy's presence in the nightclub on Saturday, but admitted that he would prefer him to have been in bed.
“They are old enough to know what they have to do," the City manager said.
"I’m not his father. I would prefer him to go to sleep earlier but I don’t control the players in that situation."
But Guardiola claimed that he was not frustrated by Mendy's actions, adding: "I’m a relaxed guy. It might not look like it but I sleep quite well.”
Mendy has only made one appearance for City since November, when he underwent surgery on a knee injury.
The France international also missed the majority of last season with a separate knee issue and has played just 20 times for City in total since joining for £52million in 2017.
Mendy was brought to the Etihad to be City's long-term first-choice left-back for years to come but Guardiola is now openly considering other options.
"If it happens in two seasons it can happen [in a third]," he said last month, referencing Mendy's dire injury record.
"The truth is we could use him only in a few games. At the end the strongest guys every day are there. That’s why we are looking for, maybe for the next season."
Mendy is now fit again following his most recent knee injury and could play a part in Wednesday's Premier League clash with Cardiff City.
Guardiola said last Friday that Mendy had recovered and was available for selection again though claimed that he needs time before he can play.
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