Manchester City are at the front of the queue to sign Napoli defender Kalidou Koulibaly.

The Citizens are insistent about signing a center back to partner Aymeric Laporte.

Pep Guardiola wants a proper crack at a third Premier League title and knows he must shore up their rearguard.

And according to transfer expert Duncan Castles, City are at the head of the fight to sign Koulibaly, as clubs like Liverpool may have other priorities.

Speaking to Ian McGarry, Castles said on the Transfer Window Podcast: "[Liverpool] want to sell Dejan Lovren - and if they do, they can bring in a new centre-back.

"They also want a back-up left-back - and one idea to solve both problems is to sign a left-footed centre-back you is comfortable at left-back.

"Their priority, though, is to sign someone in attack after missing out on Timo Werner.

"Pre-lockdown, Napoli wanted £90million for Koulibaly, but [Liverpool would prefer] closer to £50m.

"Talk from Napoli is they could be looking at around £70m now for Koulibaly."

Castles added: "The word from people close to Koulibaly is he thinks there's a strong chance he will end up at Man City.

"The noises and effort City have made so far and their greater need for a top centre-back [make it favourable to Koulibaly].

"They're short on quality at centre-back and the only option Pep Guardiola trusts is Aymeric Laporte.

"In Koulibaly's mind, it's his more likely destination this summer."