Matthew Upson believes West Ham's next four matches will define their season as Gianfranco Zola's side prepare for Sunday's daunting derby at Chelsea.

The 2-0 home defeat by Spurs left Zola's team just three points above the Premier League relegation zone, and with just four goals scored in their last 10 matches, the Hammers' lack of bite in attack is becoming a serious worry.

After taking on Luiz Felipe Scolari's side, West Ham have a home match against inform Aston Villa on 20 December, before they travel to Portsmouth on Boxing Day and face Stoke at Upton Park two days later. And England defender Upson knows the Hammers must raise their game if they are to turn things around.

He said: "There are a lot of teams right in the thick of it.

"This period building up to Christmas and the matches around that time will put a bit of distance between the teams who can move towards the higher reaches of the table and those who will be struggling at the bottom.

"So the next four games are all important for us. We have to make sure we get back to working hard. This period is huge because we can pull out a gap between ourselves and the bottom of the table."