Ricardo Carvalho says Chelsea's players must match Southend United's workrate if they're to avoid an FA Cup shock.

"It is different, this competition. It is a big day for them and you have to prove you are better, you have to run as hard as them and you have to play with the ball because you have more quality," the Portugal international told the club's official website.

"But you have to run as (much as) them. Sometimes they run a little bit more than us, they run like crazy and it is difficult - but after when our quality is coming and you prove inside you are better, normally it is one, two, three-nil.

"So let's see how it happens this time against Southend. The game will be difficult in the first 20 minutes and you have to play serious and play better than them to score goals."