Speaking on Sky Sports, Merson said, "He's phenomenal. No one really knew much about him when he came from Man City, so it was a free hit for him. But in the last seven months, he's now the big boy. The name of the game for opposition is to stop Cole Palmer.
"Teams are trying to stop him - and they can't do it. That shows you how good he is. He's too intelligent. He's always got space. Everybody needs an X-factor to win a Premier League title and Chelsea have it with him."