The Hammers will be playing only their second match of the month when they travel to Stamford Bridge, while Chelsea face six games in 16 days after reaching the quarter-finals of the Europa League by beating Steaua Bucharest on Thursday.
"It might favour us at the start of the game because we should be able to set the tempo and get into our stride quicker because we've been more used to playing competitive games recently," Hazard said.
"But where it might favour them slightly is the fact that towards the end of the game tiredness may set in for us, while in effect they should be stronger because they've had a bit of a rest.
"It's something we have to deal with, and with the support of our fans behind us I'm sure we will be able to.
"Three points are a must for us on Sunday - we need to win the match. Chelsea are a big club - we have to win titles and to qualify for the Champions League. There's a lot to do but we'll try to do it all."
Chelsea have been drawn against Russian side Rubin Kazan in the last eight of the Europa League and Hazard believes they can clear that hurdle.
"From a geographical point of view we probably would have preferred a different draw," said the Belgian. "We have to get through and playing in Russia is never an easy game.
"However, we have to make sure we do enough in the first leg to go over there and secure our place in the semi-finals."
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