Dutch great Ruud Gullit says Liverpool's success hinges on the presence of Virgil van Dijk.
Gullit believes Liverpool's capture of Van Dijk coupled with Manchester City's defensive woes are the reason why the Reds are so far in front of City in the Premier League.
"In order to win, all the best teams have a good defence," Gullit told Omnisport.
"At Barcelona, with Carles Puyol at the back, they had a good defence. If you don't have that then you can attack all you like but you're always conceding a lot of goals.
"Pep Guardiola bought four central defenders and they couldn't do it. They were unlucky also with injuries but it is a stable factor to have defenders that can do the things that you need to do."
He added: "A lot of teams don't defend well. So with Van Dijk, that was an issue that was done (solved). Van Dijk was an example that I was right in Holland. If I say you have to learn how to defend people say, 'you're always with the defending' and things like that.
"But that's where it all started. Now they say you're right, [you can have success] if you have a good defender, and the good thing is it was a Dutch defender."