Poor strength in depth
It's been covered multiple times before, but it remains a problem; Arsenal don't have effective cover in enough positions to guarantee them a strong squad when injuries and suspensions hit.
Aside from the midfield, which can boast a number of top quality players, Arsenal lack tried and trusted players who can step in when needed.
When the fixtures start to come thick and fast it's usually the teams that can field the strongest sides consistently that pick up results.
Teams like Manchester City and Chelsea are prepared for all but the most devastating of situations, but if Arsenal lose one or two men in certain positions they will be significantly weakened, and Wenger may be forced to throw on youngsters or players who aren't good enough to compete at the top.
This will definitely have a bearing on the results they pick up and therefore could leave a dent in their title hopes.