While City have recorded 14 successive wins in the Premier League, Guardiola has struggled for defenders in recent weeks, with John Stones missing a number of games with a hamstring injury and Vincent Kompany sustaining several fitness issues since August.
The 46-year-old told reporters: "We are thinking about it. In that department we have too few players and to handle all competitions we are in trouble, real trouble if this is the case. But I can't assure anything. We're going to see what will happen in January.
"Maybe we are thinking of looking at another central defender because of Vincent's problems, John Stones is four or five weeks out. And we miss an important player like Mendy."