What's caused Eden Hazard, Juan Mata to drop off and will they rebound?

When the Premier League television allocations were made prior to the 2015-16 season, this weekend's Chelsea-Manchester United match was undoubtedly the headline fixture. And while there's plenty of intrigue surrounding the showdown at Stamford Bridge, it's unlikely that anyone would have predicted it would involve teams lying 13th and fifth in the table, respectively.