City signed the defender from Borussia Dortmund on a five-year contract for a fee of around £15 million, making him their fifth signing of the transfer window which closed on September 1st.
Guardiola's side will be without Aymeric Laporte (28) for another month as he recovers from knee surgery while his fellow defender Nathan Ake (27) is fit again after overcoming a muscle injury.
"We had four incredible centre backs... Aymeric had a tough injury, he's getting better but still one month or half... Nathan had some concerns," Guardiola told reporters before Saturday's Premier League clash with Aston Villa.
"We couldn't live with just two centre backs with this schedule. We had an opportunity to bring a player with one year left on his contract, incredibly experienced.
"He is perfect for what we need... good in the build-up. We felt it versus Dortmund. (We are) pleased he's here."
Guardiola said he will not force Laporte into action before the next international break later this month.
"One month ago we said September or October. Early October. He'll be ready after the international break," the Spaniard said.
"We won't force it. Knee is a tough injury."
City are second in the Premier League table with 13 points from five games, two points behind Arsenal who have made a perfect start.
