While Chelsea may be sitting pretty at the top of the Premier League title, seven points ahead of nearest rivals Tottenham and Liverpool, all is not completely serene at Stamford Bridge.

Two weeks ago, the club had just equalled the Premier League record for straight consecutive wins in a single season with 13 on the bounce and were looking near unstoppable as they marched closer to regaining their title.

However, a 2-0 defeat at Tottenham and some issues behind the scenes have left an air of uncertainty hanging over Stamford Bridge, even if their results, bar the loss at Spurs, have continued to be good.

Main man Diego Costa appears to be at the centre of it all, as the controversial Spaniard seems destined for pastures new, or pastures richer, amid relentless talk of a Chinese Super League move. Add in the rumours surrounding the departure of Michy Batshuayi, and even players such as Ruben Loftus-Cheek, and it could be that the Blues may need to invest heavily during the remainder of the January transfer window.

With that in mind, here are THREE positions the Londoners should be looking to improve their options in...

Centre-back

Chelsea's defensive record this season has been exceptional thanks to the change in system Antonio Conte bought in with him from both the Italian national side and, of course, former club Juventus. The back-three of David Luiz, Cesar Azpiliceuta and Gary Cahill look a formidable unit and one that is likely to remain as the starting selection for the rest of the campaign.

However, what about the future? The returning Kurt Zouma will be a huge boost, but other than that the Blues have few options with both John Terry and Branislav Ivanovic seemingly no longer up to the task. Could it be that Chelsea re-call sone of their loan stars - Andreas Christensen of Borussia Monchengladbach springs immediately to mind - or do they splash the cash on say, Virgil Van Dijk?

An interesting conundrum.

Striker

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Given the drama at Stamford Bridge over the past few days, bringing in a striker this January seems a must for Antonio Conte and the Blues, regardless of whether either Costa or Batshuayi are to leave. Both are unsettled, and Chelsea need to be prepared.

Swansea's Fernando Llorente has been linked with a move, but the Londoners should really have their ambitions set a little higher. Bringing in another household name to keep those already at the club on their toes, as well as prove that the Blues are bigger than one single player in Costa, is really important if they are to really maintain their title challenge. Alvaro Morata could be one to look at, but Thomas Muller of Bayern is possibly the most high profile player to be linked with a move to London.

Wing-back

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Victor Moses and Marcos Alonso have, for me at least, been Chelsea's two star men this season. Yes, Costa has been terrific and Eden Hazard on another level, but we almost expect that from those two. What has been so fantastic about the former pair is the element of surprise.

Moses looks a new man under the guidance of Conte and his new position allows him to both work defensively but also explore his obvious attacking attributes, while Alonso appears to be a class act down the left flank. Behind them, however, there is nobody, and the role of wing-back is fairly specific, so Chelsea need to invest in the right players. Michail Antonio of West Ham has been linked with the club, as has Wolfsburg's Ricardo Rodriguez, however, it is unlikely a move for the latter would be plausible given the form of the starting pair.