Damien was making in roads into the Fulham defence and, as he shot the ball, Davis attempted to block him and ended up sending Duff up in the air for an awkward landing.
Looking in complete agony, Duff was eventually helped off the field to be replaced by Joe Cole after eight minutes.
It comes as a huge blow for Chelsea with a busy festive period coming up. First we take on Charlton on Boxing Day, followed two days later by a home game against Portsmouth. On January 3rd we travel to Watford for the thrid round of the FA Cup, followed by a midweek home game against Liverpool.
For those that can't make it to any of the above games, all but the Portsmouth match will be shown live on Sky Sports!