And why do you say they would be aiming for the league title? I mean this is even the best opportunity they have as Manchester city and arsenal are definitely losing more and more points by the day and the only team standing in their way now is Liverpool which can also slip up, I mean if anything they lost the league to city when they were already eight points clear so definitely anything can still happen with Chelsea.
Chelsea must improve their defense in January to be a contender for the Premier League title this season. They are currently Liverpool's closest rivals in the hunt for the top of the standings because Arsenal and Manchester City have been inconsistent in their last few matches.
Not just their defense, I think that the area they need someone very urgently is the goalkeeping department, Sanchez is actually a disaster in goal, and it's near impossible to win the league title with such a terrible goalkeeper.
No disrespect to Sanchez but he is actually the worst goalkeeper I have seen as the first choice of Chelsea football team since I started watching football, because not a single match that he features that he wouldn't display incompetence in goal.
So in my own opinion, the newly acquired Jorgensen should be used till someone much more better than them both is found.
Then as for the defense, I think that Chelsea just need a top central back that can lead From the back, but where the problem really is right now is the goalkeeping department.