The Attacking Midfield.
In the current Chelsea setup, I believe there is only one player in the whole team that can feel that they have a tight grip on their position. And that is Petr Cech. There are at least two players in each position that would make it into any midtable or above BPL side. Only a handful of top clubs can claim to have this strength in depth. With the depth and quality that the Chelsea squad have, coupled with Jose Mourinho's experience in the competition, many expected them to have a hand on the Premier League trophy before the season even began.
However, Chelsea have not had the best start that they could have hoped for, with unconvincing displays against Aston Villa and Fulham, they were lucky to have got away with the wins. Defeats to Basel and Everton raised questions as to whether Mourinho has tinkered too much with a Chelsea team that was beginning to find its form towards the end of last season. The problem however, has been finding the right balance, and with a squad of this size, it is very hard to try certain combinations without risking valuable points.
The main concern is the attacking midfield, by playing a 4-2-3-1 formation, only three of the seven attacking midfielders can be played at a time. A way around this is to change the formation; Mourinho has already tried playing a 4-3-3 in certain games but the performances were not convincing enough for the formation to be established. E.g Basel.
Jose did have time to tinker with the players during pre season, but due to late signings, confederation cup players and injuries, the precious time was wasted. However it was clear that Jose established one thing about his attacking midfield in pre season. He wanted Oscar as his number 10. This is a very important role in world football as the wingers and the deeper midfielders will always look to this player for creativity and the striker cannot perform without good service from the number 10. Juan Mata established himself as the number 10 for Chelsea by putting in a consistent array of dazzling performances in the blue shirt. However injury in pre season caused Jose to play Oscar in his favoured number 10 role and the young Brazilian started putting in creative and industrial performances for the team. Several eye catching displays for Brazil in friendlies and confederation cup games may have also influenced Jose’s decision to play him in this role. His defensive contribution has also caught Mourinho's attention and is clearly a quality that the Portugese manager is trying to implement in his other offensive minded players.