Cristian Romero's future at Tottenham is set to be the subject of plenty of speculation this summer and the club will need to have a succession plan in case the Argentine does leave.
The 27-year-old has been linked with a move to La Liga after admitting a desire to play in Spain before his career ends and Atletico Madrid boss Diego Simone has made no secret of wanting to sign Romero with his public statements about the World Cup-winning centre-back.
With two years left on his contract, the Argentine is in an awkward position where Spurs have to make a decision on his future but can also ask for a huge fee still for a player Lionel Messi called the best defender in the world, and that price tag could be the sticking point for many clubs like Atletico.
Romero struggled with injuries last season, mainly with his foot, and took part in only 18 Premier League games. However, he starred in the Europa League and was named player of the tournament and player of the match in the final in Bilbao.
It remains to be seen whether any team gives Tottenham something to think about with a serious offer when it comes to the two-time Copa America winner, but if they did then new head coach Thomas Frank will need to think about who comes in for Romero.
Here are five potential candidates to step into Romero's considerable boots.
Marc Guehi
The most obvious candidate in the transfer market would be Crystal Palace captain Marc Guehi, who Spurs have admired for a long time and made an approach for late in the January transfer window. That was rebuffed by the Eagles, who had no real time to get in a replacement for the England international at that point.
Now Guehi has just a year remaining on his contract so Palace will have to decide if this is the summer in which he finally departs or risk losing the 24-year-old for nothing. The problem for Spurs is that while they can offer Champions League football next season, all the big clubs would love to have the England centre-back and Liverpool and Arsenal are both very keen.
If clubs can agree a fee then Guehi is expected to make his decision based on the amount of game time he will get. If Romero were to leave then Spurs would be able to offer plenty of that and probably plenty regardless if he remained, but due to the number of centre-backs at Tottenham at the moment, they might not make a move until the exits are clear and by then Guehi, who can play anywhere across a back three or central pairing, could be gone.
Kevin Danso
Spurs would sign another centre-back if Romero departs regardless, but Kevin Danso could also push his claims under Frank to become the new leader of the backline.
The Austrian has a strong personality and showed plenty of promising moments in his first four months of the season despite being thrown straight into a difficult situation. The 26-year-old also showed some wasteful moments with the ball, but will likely have less pressure on him to play some of the passes or make the dribbles that Ange Postecoglou's system called for.
Danso, who played an important late role in the Europa League final in Bilbao, is a strong character and leader and is already popular in the Spurs dressing room. He can fit into a back three as well, and he and Frank are likely to hit it off early on due to their similar mentalities, which could put him in a good position to take advantage if Romero departs.
Nathan Collins
Frank might look back to someone he trusts at Brentford and the most Tottenham-type signing among the centre-backs is probably Nathan Collins. The Republic of Ireland international, who only turned 24 under two months ago, came on leaps and bounds under Frank and became a key man in his defence.
The Dane said midway through last season of Collins, who played on the right of his central defensive pairing: "He got that injury [the previous season] and got that setback. He struggled to get back up to pace and made some mistakes, which didn't help his confidence. At the end of last season, he was more or less back to the good start he had.
"Now he has more consistency and his composure on the ball is good. He can find passes in the pockets, the diagonals and the balls in behind. He is very good. This year, he has made some crucial blocks, defending the goal and the box very well. He has just got more consistency in the way he plays.
"Another important thing is the concentration. I think his concentration levels have gone up and the best players in the world have got the ability to concentrate for 90 minutes."
The problem for Spurs is that Collins has a long contract until 2029 and would not come cheaply. However, if they got big money for Romero then the young Irishman would be able to come in and slot straight into Frank's system after some big displays for the Dane across the last campaign. He would be less of a risk than many foreign signings they might look at in the market.
Luka Vuskovic or Ashley Phillips
There could also be a breakout star in defence under Frank with the new head coach always looking to give young players a chance after his formative years as a coach in the Danish international youth set-up.
The Dane will not have made any decisions yet over the young players as he will want to take a close look at a number of them during pre-season to decide who is ready for his team and which ones must head off on loan again or out of the door permanently.
Luka Vuskovic will finally arrive at Tottenham after two loan spells before being able to join officially after his 18th birthday. The teenager has been a star in Belgium with Westerlo and Spurs beat plenty of Europe's biggest sides to land the Croatian starlet, no doubt with the promise of first team minutes if he impresses.
That will be on Vuskovic this summer but he's certainly got heaps of potential and could be given until at least January to settle in. Spurs' pesky club-trained issues might make it difficult to name the teenager in the Champions League squad, depending on the future of Romero and Ben Davies, but he could get game time in the Carabao Cup to begin with.
The same goes for Ashley Phillips, who could not get a look-in under Postecoglou but has impressed on both his loans to Plymouth and Stoke in the past couple of seasons. Frank might be impressed this summer by the young defender, who turns 20 on Thursday, and that could change what comes next for him. The next move for Alfie Dorrington must also be decided as well after he became a Scottish Cup winner with Aberdeen.
Jarrad Branthwaite
Another big money potential arrival would be Everton's Jarrad Branthwaite with the centre-back, who turns 23 on Friday, linked with Tottenham in recent weeks.
The Toffees defender, who has made one England appearance, has been the subject of interest from Manchester United in the past with a huge price tag on his head because he still has two years left on his deal with an option for a further 12 months.
The other issue for Spurs is that Branthwaite would not be a straight Romero replacement in terms of where he would play on the pitch, because like Micky van de Ven, he is a left-footed centre-back who operates on that side of the defence.
He and the Dutchman would likely be an awkward pairing so while we're adding him as a potential option to replace Romero in the squad, he would not likely replace him in the team.