Everton solved one area of their defence with the signing of centre-back Michael Keane in the summer, but on the other side of the pairing they still have room to improve.
Ramiro Funes Mori is a long-term absentee after suffering a serious knee injury, Ashley Williams’ errors are becoming increasingly costly as the Toffees search for form, and Phil Jagielka is, at 35, on entering the twilight of his career at Goodison Park.
Given that many top-flight clubs are now playing three at the back, any new signings need to be versatile in this regard.
While the club will primarily be looking for a centre-back to play on the left of the pairing in a back four, they should also bear in mind that any future manager may also want to play with a back three.
Certain centre-backs can struggle when asked to play in the wide areas on either side of a trio, so this player needs to have some of the qualities of a defensive full-back, given that’s the position on the pitch they often find themselves in when operating in this system.
The level of these targets depend on the club’s ambition, but since the takeover of Farhad Moshiri as their majority shareholder, the announcement of plans for a new new stadium, and the lavish summer spending, Everton are edging closer to the top end of the transfer market. There are a couple of players among the following bunch whose signing would be a real statement of intent.
Napoli’s French centre back is one such player. A move for the 26-year-old would mean the Toffees are shopping at the high end of the European market, and bringing him in could be a game changer both in terms of the club’s profile and the quality they possess at the back.
The 6ft 5ins left-footer has one of the best pass success rates in Europe, not just for centre-backs but for any position, with 93 per cent. After just seven games this season he already has one assist and two goals to his name, and he only makes an average of two clearances per game.
While some algorithms have clearances down as a positive stat for defenders, having a high number in this column can sometimes suggest a panicky defender who punts the ball away at the earliest opportunity. While Napoli's system and dominance in possession helps with this, Koulibaly also helps them play such a system.
Given Everton have been so tentative at the back, combining aimless passes with panicked clearances, the Frenchman would improve them instantly.
The Mexican recently moved to Roma to replace Antonio Rüdiger, who made his way to Chelsea, but if a club put the right offer on the table then the Italian side could be open to a sale.
The 29-year-old is one of the more experienced players on this list, and is likely to star for his country at the 2018 World Cup after they qualified with ease. He’s found himself behind Kostas Manolas and Federico Fazio in Rome, which is another reason for Everton to think they have a chance of signing him, even if the initial move is only a loan.
He can operate on either side of the defence, but being left footed he’s more natural on that side. In his last season at PSV Eindhoven before his move to Italy, he managed an impressive seven goals in 32 league games.
The Bilbao man, like compatriot Koulibaly, is a tall elegant centre-back whose main strengths lie in his ability to pass the ball out from the back.
Everton will be looking for composed ball playing centre backs as part of their desire to become a team which dominates game. The possession game starts from the back, and 23-year-old Laporte would be an ideal signing.
While his team don’t dominate games as Koulibaly’s do (52 per cent possession as opposed to 61 per cent), he still has a reasonably good pass success of 86 per cent in the league. This number should improve as the season goes on and there are more games from which to take the average.
As well as playing on the left of a central pairing, he could also be effective as a ball-playing sweeper in the middle of a back three.
The Hamburg native has long been on the radar of clubs across the continent, but as of yet he hasn’t made the move away from the Bundesliga. He did, however, move from his hometown club to Bayer Leverkusen in 2015 and has impressed, aside from a period of inconsistency which could have been caused by injury problems last season.
Tah is right footed, but has played on the left of defence in the past. His size and aggressiveness when defending give way to a calm and composed player on the ball, and he has a pass success of 88 per cent so far this season.
The 21-year-old will look to build on his better performances, and an impressive season in Leverkusen could see him back on the radar of Europe’s top clubs. Everton would do well to get in early, and snap up the versatile centre-back before the rest come calling.
He represented his country throughout youth level, but despite the likes of Keane, Harry Maguire, and John Stones all securing caps in recent years, and the latter becoming a key part of the first team, Gibson remains uncapped.
He was called up for the England squad this summer, but didn’t make it onto the pitch. Now back in the Championship with Boro, a securing that first cap is even harder to achieve.
A move to Everton in January could boost his chances of a call-up, but he might want to see if he can get his local club back in the Premier League first, although Middlesbrough are only 11th in the Championship at the time of writing.
Another left-footer, the 24-year-old would slot in perfectly alongside Keane, and could probably do a job in the middle or on the left of a back three.
He already has a goal and an assist to his name in the Championship this season, and is likely to be more of a realistic option than the other players mentioned, though he could come with the English player premium on his price-tag.