The Blues would have expected to maintain their three-point advantage over fifth-placed Arsenal, but a Jamie Vardy goal gave the Foxes all three points at Stamford Bridge.
Chelsea are now 11 points adrift of leaders Liverpool, and Maurizio Sarri will be aware that his side require a win at Vicarage Road.
Sarri has a number of selection dilemmas ahead of the game on Boxing Day, and here Sports Mole looks at how his team could line up against the Hornets.
Sarri could also make alterations in defence in order to cope with the busy festive period, with Gary Cahill a potential inclusion in the centre of the backline.
Alvaro Morata has returned to training after a knee injury but will only be considered for the bench, while Andreas Christensen will sit out the game with a minor hamstring injury.