The former Crystal Palace captain moved to City yesterday for £30m, signing a deal to 2031.
Guardiola said: "Top central defender, played for the national team. I will say my personal thanks to the club,” the boss said in his pre-match news conference.
“He is the perfect age for many years, he can play right or left. And him especially because he wanted to choose us.
“The problem we have at the back in the next few months so it’s really important that he is here.”
Speaking ahead of their Champions League tie with Bodo/Glimt, Guardiola says a solid back four is key to any success this season.
He also said, “We make seven wins in a row, it’s because we have Matheus (Nunes), Ruben (Dias), Josko (Gvardiol) and Nico (O'Reilly), playing games and that gives you consistency.
“I love to rotate the team but when you have a consistent back four, it helps. When you have a situation like we have right now, it is normal we have some ups and downs.
“Accept it. It happens. Ait-Nouri listens to a lot of things. Not even one year, Khusa is here, Max Alleyne a few weeks. We accept who we are and try to be better in the next games.”