1) Lack of English players
This is a long term issues, but the departure of Frank Lampard and Ashley Cole in the summer leaves only John Terry and Gary Cahill as English players in the first team. John Terry probably only has one year left in him (though we seem to say that every year), so Chelsea are in desperate need of English players to fulfil their various domestic and European quotas.
There are of course the young players – Dom Solanke, Izzy Brown etc – who are apparently going to be playing in the first team soon, but we’ve heard this every year since Terry broke into the first team, so nobody is holding their breath.