Chelsea suffered a setback in their title challenge on Saturday, when they lost 3-2 to Stoke City. With Arsenal's failure to capitalise against Everton on Sunday, the loss is not as devastating as it could have been. However, the real worry is that in Chelsea's last three games, they have conceded a total of seven goals.
It brings to light a problem that has been largely overlooked so far this season. With much of the focus on the need for a new striker, many people have missed the fact that it is defensive inconsistency, not striking problems, that will cause the Blues the biggest problems in their hunt for a Premier League title. After all, Chelsea have scored 12 goals in their last four Premier League games.
With that in mind, here are some of the best candidates to bolster the defence at Stamford Bridge.
The Mirror is reporting that this £40 million-rated French defender, rumoured to be attracting plenty of interest from clubs like Chelsea, has recently switched agents to facilitate a deal in January.
Whether this is true or not, the 22-year-old F.C. Porto player would undoubtedly be a solid addition to the Chelsea defence. His athleticism and physical style would be a perfect fit for the Premier League, and he was at the centre of a Porto defence that only conceded 14 goals in 30 games last season.
At such a young age, he would also be the perfect long-term successor to John Terry. The price is steep, but since Chelsea might not be going for a striker, Mangala could be a good investment.
In another rumour courtesy of The Mirror, Jose Mourinho is reportedly ready to offer £10 million for the French defender from Saint-Etienne.
At just 19, Zouma is even younger than Mangala, but he also comes with some baggage. He is currently serving a 10-match ban for a leg-breaking tackle.
However, you might be able to put some of his bad-boy reputation down to youth, and he could benefit from the firm guidance of Mourinho. He is also a quarter of the price of Mangala. That is good business, even if they don't use the extra money for a striker.
So there we have it. Three of the best, most realistic options for Chelsea this transfer window. It is clear that the Blues need at least one more defender, but who will it be? Put forward your own suggestions in the comments section.