If you’ve watched Chelsea for more than 15 seconds this season, you’ll have seen just how much the Blues need an upgrade at centre-back this summer.​

There are a few different routes Chelsea could go down here:

1. Sign an experienced star.

2. Sign a slightly younger defender who is already on track to become a star.

3. Sign a youngster who has the potential to become a star.

It remains to be seen which avenue Frank Lampard and Co. will choose to explore, but here are eight centre-backs who Chelsea could consider this summer.

Kalidou Koulibaly (Napoli)

Kalidou Koulibaly

It seems like every big club in Europe has been linked with Kalidou Koulibaly for years, but you get the feeling that all the ​speculation could finally be coming to a head this summer.

If you need a good defender (and ​Chelsea really do), there are few better options to turn to than Koulibaly, who has been among the world’s elite for a good few years now. He’s powerful, agile and deceptively gifted with the ball at his feet.

With a focus on spending big on centre-back, Chelsea have already taken a good look at Koulibaly. His €100m asking price is expected to be lowered slightly in the aftermath of ​Napoli‘s implosion earlier this season, so he is relatively affordable. You know, all things considered.

The main concern is that he will be 29 in June, and given Chelsea don’t usually offer anything more than a one-year contract to anyone over 30, to see them spend so much money on Koulibaly would be more than a little out of character.

Having said that, the Blues’ need for stability at the back makes this situation slightly different, and spending big money at the back is probably a wise idea.

Potential Price: £65m – £90m

Alessio Romagnoli (AC Milan)

Alessio Romagnoli

At 25 years old, ​AC Milan‘s Alessio Romagnoli falls into that second bracket. He’s a real talent and still has plenty of time left ​at the top. Is that the dream?

Milan have been in a state of constant transition ever since Romagnoli arrived, but the Italian has survived it all. However, all that upheaval has not gone anywhere, and it may just be time to call it quits this summer.

There have been a whole load of reports (including ​this from Nicolò Schira) coming out of Italy suggesting that Milan need to sell to fix their financial problems. Goalkeeper Gianluigi Donnarumma has been touted as a potential casualty, but Romagnoli could be a feasible alternative.

He still sort of fits in with Chelsea’s younger vibe these days, but he comes with around 200 ​Serie A appearances and a handful of international caps to boot. That’s a combination that Chelsea should not pass on.

Potential Price: £35m – £50m

Nathan Aké (Bournemouth)

Nathan Ake

​Nathan Aké used to play for Chelsea! He should go back because all his academy teammates are there!!!!!

Right, now that’s out of the way, let’s look at this one properly. Aké is by no means the ​Premier League‘s best defender, but he definitely has something about him – links to ​Manchester United and ​Manchester City prove that.

His top-flight experience would be a huge help to the Blues’ side, but so would his versatility. The 25-year-old is comfortable out at left-back, which is another of Chelsea’s problem positions. He could fill two gaps in the squad.

Chelsea let their buy-back clause expire in January, so they would have to agree a traditional transfer if they wanted him, but that might not be too difficult. Bournemouth have been flirting with relegation this season, and if they can’t avoid the drop, Aké would suddenly become a whole lot easier to sign.

Plus, let’s not act like his former attachment with the club isn’t worth noting. He wouldn’t need much time to adjust and would fit in with the rest of the group relatively quickly. It’s perhaps the simplest option out there.​

Potential Price: £40m – £50m

Dayot Upamecano (RB Leipzig)

Dayot Upamecano

The fact that everyone, their neighbour and their dog want to sign Dayot Upamecano this summer tells you exactly why Chelsea need to fight their way to the front of the queue for his signature.

He’s only 21 years old, but he has proven himself as one of the ​Bundesliga‘s top defenders with RB Leipzig. That would be enticing enough on its own, but the fact that he will enter the final year of his contract this summer takes the whole thing up a notch.

​The Daily Mail are one of thousands of outlets to confirm Upamecano comes with a £55m release clause, which is about as affordable as you’re ever likely to find in today’s market – especially for someone with such high potential.

He would be an instant upgrade on any of Chelsea’s current crop of defenders, and he could keep his spot in the team for the next decade. That’s a smart bit of business.

Potential Price: £55m

Gabriel Magalhães (Lille)

Gabriel Dos Santos Magalhaes

Now we’re approaching those who are a little more about potential than current talent. First up is Lille’s ​Gabriel Magalhães, who has enjoyed a breakout year in France.

The Brazilian looks like a little more of a risk, given he has just 18 months of top-flight experience under his belt, but he has looked more than good enough to justify all the hype around him.

Lille are always willing to sell for the right price, so this is a deal which could happen with relatively little stress, but you have to ask yourself whether he is a major upgrade on any of Chelsea’s current defenders.

He’s young with relatively little experience, which is the entire story of Lampard’s squad this season. He’s not the kind of blockbuster name which the boss might want, but what Gabriel has is the potential to get there.

Potential Price: £25m – £35m

Marash Kumbulla (Hellas Verona)

Marash Kumbulla

Marash Kumbulla’s story is similar to Gabriel’s. The Albanian has had one strong season in ​Serie A​ and has convinced scouts from a number of top sides that he could be one to watch for the future.

The 20-year-old has impressed against some of the division’s top sides, helping Verona avoid defeat against both ​Juventus and Lazio since moving into the starting lineup. He’s young, but he’s still holding his own against elite competition.

​Inter and Manchester United have both been linked with him, and it’s likely that he’ll be on the move at some point in the near future. As long as the price is right, it could be a risk worth taking.

However, of all those with top-flight experience on this list, Kumbulla brings the least. He still has plenty of work to do, but Chelsea could be the ones to lead him to stardom.

Potential Price: £25m – £35m

Ben White (Brighton & Hove Albion)

Ben White

Ben White’s development out on loan with ​Leeds United has been one of the most exciting stories of the Championship season. The 22-year-old has been fantastic for Marcelo Bielsa’s side, and he will almost certainly be playing in the ​Premier League next season. But with who?

Because he’s young and English, links to Chelsea have come as no surprise, and it would hardly be the worst deal for the Blues. White has looked good in the second tier, and as Chelsea can tell you better than anyone, that might mean he’s ready for a top Premier League side.

Having said that, we’ve seen countless players fail to make the jump to the top division, so moving for White would be an enormous risk. He could blossom into a superstar or fade away into obscurity.

As far as youngsters go, White is one of the best that England have to offer. His appeal is clear to see, and he may prove to be the answer to Chelsea’s questions.

Potential Price: £18m – £25m

Mohammed Salisu (Real Valladolid)

Mohammed Salisu

Ghanaian centre-back Mohammed Salisu has earned rave reviews with Real Valladolid this season. Given his side are down towards the bottom of ​La Liga, he’s had a lot of work to do, so there have been plenty of chances to impress.

He’ll be 21 by the time this summer arrives, ​so he has the potential to be a cornerstone of the team for the next decade, but that’s only if he lives up to the hype which has built around him already.

Dubbed ‘The Wall of Valladolid’, Salisu is an enormous physical presence with impressive technical ability, so he has all the attributes to make it as a top defender. Will he get there? We’ll have to wait and see.

However, the best has been saved until last. His release clause? Well, according to ​Marca​, it’s just €12m. In today’s market, that’s pocket change.

Potential Price: £10.5m

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