Guardiola, who has guided City to two Premier League titles, three League Cups and the FA Cup following his arrival in 2016, signed a new two-year deal on Thursday that will keep him in charge until the end of the 2022-23 season.
"Right now Messi is a Barcelona player and the transfer market is in June and July", Guardiola added.
With the global fixtures of the year done, a gruelling winter schedule of club football awaits for England's top-flight with nine rounds of league matches before January 2.
"We still have the feeling we have many things to do, because the squad had the feeling we are comfortable being together and try to do what we have done the previous seasons".
But Barcelona fans have been left concerned about his commitment to the club after an outburst following arrival back in Spain from a Champions League fixture. That is the only thing in our mind.
Guardiola said: "Messi is a Barcelona player".
After all the debate about his future, all the uncertainty about this potentially being his final season in the Premier League, Guardiola has signed a new contract and is already talking about winning more trophies.
"And I think he is happy for the journey to continue". It will be good to do what we have done the last three years, but it's hard. "The rest I can not say anything else".
City return to action following the worldwide break at Tottenham on Saturday.
Guardiola said: "Sergio was training this week and Raheem, today was the first training with the team". It's simple." The manager then said, "So I'm here and continuing because we have had incredible success, a year ago won two titles. "In Christmas, we will again play twice in less than 48 hours and we'll have this discussion again".
"We saw the statistics here in the United Kingdom and it's rising every day. Don't ask me because I'm nearly 50, so I'm old enough to understand".