Chelsea's Antonio Conte has admitted his surprise at seeing Saturday's opponents West Ham United down the Premier League table.
West Ham are without a win since September and go into their lunchtime meeting in 19th place.
"They have a lot of good players with great talent," the Chelsea manager told the club's official website. "Also this is a very physical team. For sure they have the potential to do better.
"In their last game, I saw Manchester City struggling a lot before they won.
"It won't be easy. And it's a London derby. We must pay great attention."