City currently have four senior centre backs with John Stones, Nicolas Otamendi, Vincent Kompany and Eliaquim Mangala.
However Stones is currently out with a hamstring injury, while Kompany missed the mid-week win over Swansea City with a minor muscle problem.
Southampton’s Virgil van Dijk and Real Sociedad’s Inigo Martinez have both been linked with a move to the Etihad Stadium, with Guardiola responding to the rumours at a press conference on Saturday.
"We speak about (January signings) with the club and Txiki Begiristain (the club's director of football). We have just three guys in central defence," Guardiola said.
“We don’t want to sign someone for a few months. We want to sign them for years and we have to make sure it’s the right guy."
Guardiola confirmed England's Stones was progressing well, while Kompany will likely miss Sunday morning's match against Tottenham.
“He’s much, much better,” Guardiola said. “I think he’s at four weeks (of his recovery). The doctor said he would be out between four and six. In one or two weeks, he will be ready.”
“(Kompany) has a little problem,” Guardiola added.
“I don’t know if tomorrow he will be fit, but hopefully in the next days he will be ready.”
City are 11 points clear at the top of the Premier League after winning a record 15 games in succession. They are being talked about as one of the best teams of the Premier League era, yet Guardiola believes there is room for improvement.
"It's important to play better -- that is the most important thing,” he said.
"The record will always stay there until one day it is broken. I am happy not with the results but the way we play. Statistics are good, but I have the feeling we can be much, much better."
