With the transfer window in full swing, WhoScored.com analyse the top targets for teams across the continent.
Following on from the list of in-demand goalkeepers, it's now time to look at the defenders.
Virgil van Dijk - Southampton
Virgil van Dijk is widely considered the best centre-back outside the Premier League's top six, if not the league as a whole. The towering Dutchman is unsurprisingly attracting interest from the best teams in the English top-flight, with Liverpool, Chelsea and Manchester City all monitoring his situation closely.
He is one year into a six-year deal he penned last May, so Southampton are under no pressure to sell, meaning they can demand upwards of £60m.
The Reds were believed to be leading the race to secure his services, only to U-turn after Saints threatened to report them for tapping up the centre-back. Nevertheless, interest in the defender is understandable.
Of the 165 players to contest 100 or more aerial duels since the start of the 2015/16 Premier League season, Van Dijk has the best aerial success rate (74.4%). A WhoScored.com rating of 7.43 was among the best centre-backs in England's top tier last term.
Alex Sandro - Juventus
Brazil head coach Tite has an abundance of talent at left-back in Marcelo, Filipe Luis and Alex Sandro, so much so that the latter has only seven senior caps to his name. Nevertheless, the Juve man is widely considered one of the finest in his position in world football, with Chelsea closing in on his signature.
Antonio Conte's decision to switch to a three-man defence means quality service from wing-back is required and while Marcos Alonso impressed last season, the Juventus ace is perhaps a step up on his Spanish counterpart.
Indeed, Sandro earned a better WhoScored.com rating (7.63) than any other left-back in Europe's top five leagues last season, while he has made more accurate crosses (60) than any other defender in Serie A since August 2015.
Dani Alves - Juventus
Sticking with the Old Lady, Dani Alves looks set to leave the Turin giants this summer after a solitary season under Max Allegri. The Brazilian played a crucial role in Juventus' progression to the Champions League final before they fell at the final hurdle to Real Madrid. Like compatriot Sandro, Alves has been linked with a move to Chelsea, while Manchester City have also been tracking the experienced right-back, with a reunion with Pep Guardiola on the cards.
Only Toni Kroos (33) made more key passes than Alves (31) in the Champions League last season, with the Brazilian's attacking input vital in their progression to Cardiff. The 34-year-old also earned a better WhoScored.com rating (7.28) than any other right-back in Europe's top five leagues last season, with the former Barcelona star proving that age is but a number.
Available on the cheap, a player of his ilk and winning mentality is exactly the reason why Chelsea and City are monitoring his situation.
Kyle Walker - Tottenham
Like Alves, Kyle Walker is another right-back linked with a summer switch to Manchester City. The England international supposedly wants out of Tottenham, with the north London side setting the asking price at £40m. While that may seem excessive, Walker is first choice right-back for the national team, while no defender registered more assists in the Premier League last season (five).
He affords the attacking influence from deep that Pep Guardiola favours, with Spurs head coach Mauricio Pochettino turning him into one of the finest in his position in his three years at White Hart Lane. That being said, if Tottenham had to sell any first team regular, chances are they would sanction the sale of Walker.
Kieran Trippier has proven an able deputy and could be relied upon to step into a starting role next season.
Hector Bellerin - Arsenal
Barcelona's desire to secure a new right-back this summer could see them come full circle as they bid to bring Hector Bellerin back to the Nou Camp.
The 22-year-old left the La Liga side for Arsenal in 2011, but the Blaugrana are keen to bring him back to Spain, with current right-back options Sergi Roberto and Aleix Vidal flattering to deceive. A team of Barcelona's ilk is expected to dominate opponents and Bellerin would play a crucial role in helping stretch sides.
He's completed more dribbles (108) than any other Premier League defender since August 2015 and while his form dipped last season, that in part owing to injury, Bellerin remains one of the most highly-rated players in his position in England.
Arsenal hold all the cards in any potential transfer, though their failure to qualify for the Champions League could see Bellerin look to move away to continue his development under Ernesto Valverde. His offensive output would certainly strengthen Barcelona's right side.
Kalidou Koulibaly - Napoli
Kalidou Koulibaly was at one point top of Chelsea's wish-list last summer before the Blues ultimately signed David Luiz on Deadline Day. The powerhouse centre-back was again impressive for Napoli last season, with the Blues once more registering an interest in the 26-year-old.
Conte looks to his defenders to play the ball out from the back, with Koulibaly excelling having made the second most forward passes (1000) in Serie A last term.
His physical presence means he'd suit the rigours of Premier League football and undeniably improve any defence. Napoli, though, would be loath to losing Koulibaly on the back of another commendable campaign under Maurizio Sarri.
Stefan de Vrij - Lazio
Had it not been for a serious knee injury sustained in September 2015, Stefan de Vrij could well be considered one of the finest in his position on the continent. The 25-year-old made up for lost time last season, making 27 league starts as Lazio exceeded expectations to finish fifth in Italy's top tier. His respectable form at the heart of the defence has attracted interest from Liverpool and Juventus, who are aware the Dutchman has just one year left to run on his current deal.
De Vrij is also reluctant to extend his stay at the Stadio Olimpico, heightening the chances of signing the Dutchman. Lazio are keen to keep the centre-back in Italy, with De Vrij making more interceptions per game (2.2) than any other Lazio player last term.
For a team looking to improve at the back, the Reds would be wise to shore up their interest in the Netherlands international, even if it means missing out on compatriot Van Dijk.
Leonardo Bonucci - Juventus
For the second successive summer, Leonardo Bonucci is being linked with a switch to Chelsea. While Juventus were reluctant to cash in on Bonucci last year, there is growing optimism that the Blues could land the 30-year-old this summer.
Bonucci played more accurate long balls per game (7.9) than any other outfield player in Serie A last season and his expert distribution qualities are a key reason why Conte is so desperate to land his compatriot.
Chelsea will need to spend big to lure him away from Turin but Conte seems willing to part ways with around £60m. That could be enough.
Ricardo Pereira - FC Porto
Tottenham will likely move to replace Walker should he depart for Manchester City despite the emergence of Trippier.
Ricardo Pereira has established himself as a key man for Nice during his two-year loan spell in France, with his performances in the Cote d'Azur not going unnoticed.
Parent club FC Porto are supposedly prepared to cash in on the Portuguese right-back, though Spurs could face competition for his signature from Bayern Munich and Borussia Dortmund.
His versatility down the right would be a bonus for Pochettino, who experimented with a three-man defence last season.
Pereira's ability to play as a wing-back means he'd make for an astute replacement for Walker. The 23-year-old also averaged 2.9 tackles and 1.3 interceptions last season and is not one to shirk his defensive responsibilities.
Marquinhos - PSG
PSG centre-back Marquinhos has routinely been linked with a move to Barcelona, though Manchester United have also been credited with an interest in the young defender.
David Luiz's departure from France last summer presented the Brazilian with a chance to consolidate a regular first-team spot and he made the most of it, making 27 league starts under Unai Emery.
He didn't let his manager down when given the chance, with a 93.6 per cent pass success rate the fourth best in Ligue 1 over the campaign.
Barcelona would perhaps be the ideal destination considering their approach, allowing Marquinhos to exhibit his passing capabilities.
And Jose Mourinho has moved quickly to strengthen his defence already, adding Victor Lindelof from Benfica.