Guardiola, who was speaking at his press conference ahead of facing Chelsea at the Etihad Stadium on Sunday, was informed by a journalist that Mendy - who remains sidelined through injury - appeared to be in Hong Kong, judging by a post on his Instagram Story.
Guardiola was left nonplussed on Friday, saying: 'I don't know. 'I didn't know. F***!
Asking the press officer, Guardiola said: "Did you know?"
Guardiola replied, "Well before, he said "I'm going one day to Paris".OK, but Hong Kong is far away". "I have to understand Instagram".
On reporter's inquiry about Mendy, who is now recovering from a knee ligament injury that has sidelined him since November, Guardiola laughed at the report and even queried a club press officer to see if he had any ideas.
Pep continued: "Yesterday he was in Barcelona". "He needs to re-adapt, if you start training in two days you are fit, he has to handle the effort we are putting on him - he has to be careful".
"It will definitely not be okay if he is Hong Kong."
Mendy was in trouble earlier this season when he was late for a rehabilitation session at the training ground, having been at boxing match in London the night before.
"I was just joking with my Uber driver, I don't want no problems Pep", he tweeted.
Manchester City are now at the top of the table, but Liverpool have a game's advantage after Guardiola's side played against Everton on Wednesday night. Guardiola also responded to Aleksander Ceferin after Uefa's president claimed City lacked class for failing to attend a meeting this week regarding VAR. 'Liverpool are exceptional. I don't have the feeling (Jurgen) Klopp, (Virgil) Van Dijk, (Mo) Salah and Sadio (Mane) feel pressure.
Pep Guardiola and his team are approaching their Premier League games like cup finals.
"Thank you so much, but the Madrid supporters think they are", he added.