Manchester City manager Pep Guardiola has ruled out making any new signings in the January transfer window.
City, who play Burnley on Tuesday, have not kept a clean sheet in their last seven games and are 11 points behind Premier League leaders Liverpool.
There has been some surprise at veteran Brazilian midfielder Fernandinho being deployed in defence this season.
"I like Fernandinho playing in that position a lot," said Guardiola. "I prefer him there. That's why he plays."
City's central defence appears to be a clear area of weakness - they failed to buy a replacement for skipper Vincent Kompany in the summer, lost Aymeric Laporte to injury and have opted not to play Nicolas Otamendi and John Stones together in any game since September.
It will not prompt Guardiola to strengthen his squad in the transfer window, though. Instead he intends to stick with 34-year-old Fernandinho as his first-choice centre-half.
"I don't want any players in January," Guardiola said.
Although Fernandinho has spent all his career as a midfielder - including more than six years and 250 appearances at City - Guardiola reacted tersely when he was asked why the Brazilian was used in defence more often than Stones and Otamendi, who cost a combined £79.5m.
Asked what defensive qualities in particular Fernandinho has, Guardiola said: "Have you watched the games?"
Nevertheless, as with Spain midfielder David Silva, Fernandinho's contract will expire in the summer.
Silva has already said he will leave the club this summer. There has been no such announcement about Fernandinho, suggesting a new contract will be offered.
"We will decide on that situation at the end of the season," Guardiola said. "That is for the players who have finished their contracts and the players who have them.
"We will do what we believe is best for the club and the organisation for next season."