The Citizens are four points behind league leaders Liverpool heading into the second half of the season.
But Guardiola believes he can catch the Reds without reinforcements.
He said: "Sometimes we have done [made January signings].
"But normally, we buy one player, it's for the next five, six years - and normally these kind of situations in this transfer window don't happen.
"For loan players, maybe it can happen, but I think the big clubs don't buy players for just five or six months, and they don't sell in that period.
"If you don't have injuries, if you are satisfied with the players, the squad you have, you go with them."