The transfer window has opened in England and there has already been rampant speculation about the future of some of the hottest properties in the game.
Transfer fees are rising every summer and there may be some record-breaking fees paid in the coming window.
Eredivisie - Matthijs de Ligt
The Ajax academy product has been quite possibly the most talked about transfer subject of the season. He has had an outstanding campaign, helping guide Ajax to their first league title since 2014, winning the Dutch Cup and leading them on their improbable run to the Champions League semi-final. He has also established himself as a first choice centre-back for the Netherlands and has been integral to them reaching the Nations League finals. He won the Golden Boy award for 2018.
He was named captain of Ajax at just 17 and his performances have attracted the attention of many of Europe's top clubs. He has been heavily linked to Barcelona, where his Ajax teammate Frenkie de Jong has already agreed a transfer to. Manchester City, Manchester United, Juventus and Real Madrid are also reportedly interesting in signing the Dutchman.
With excellent technical ability, physicality and strong leadership skills at just 19 years of age, it easy to see why De Ligt is in such high demand. Very few centre-backs in world football possess the all-round qualities that he does, and he has shown that he is capable of thriving at the highest level, putting in outstanding performances as Ajax knocked out Real Madrid and Juventus in the UCL.
A reported transfer value of £63m means that any potential move would make De Ligt one of the most expensive defenders in the history of the game.
Primeira Liga - João Félix
João Félix has lit up the Primeira Liga this season, scoring 15 goals and providing seven assists in 26 appearances in just his first season in senior football. His performances were crucial to Benfica winning the league.
The 19-year-old has fantastic close control, dribbling, vision and is a clinical finisher. His composure in front of goal belies his tender age and he was vital to Benfica's run to quarter-finals of the Europa League.
In April 2019 he became the youngest player ever to score a hat-trick in the Europa League when he netted three times against Eintracht Frankfurt.
His form understandably alerted top clubs around Europe, with Atlético Madrid, Real Madrid and Manchester United all reportedly interested in securing his services. He has a release clause of €120m, and any potential transfer is likely to make him the second most expensive teenager ever.
Ligue 1 - Kylian Mbappé
At 20 years of age, Kylian Mbappé has already had a career that many players would dream of. He broke onto the scene with AS Monaco, scoring 26 goals in 44 appearances in 2016-17 season, helping them win the Ligue 1 title against all odds and ahead of the mighty Paris Saint-Germain.
Mbappe's lightning pace, movement and finishing ability made it clear that he was a once in a generation talent and his name was starting to be linked with big clubs across Europe.
Ironically, Mbappé would then leave Monaco for PSG - his hometown club - the following season, in a deal where he would spend a campaign on loan before signing permanently for a reported £166m.
Mbappé won the domestic treble with PSG in his first season and was named in the France squad for the World Cup. He proceeded to have an outstanding tournament, scoring four goals to help guide France to their second World Cup triumph.
The 20-year-old won the Best Young Player award for the tournament as well as being named in the World Cup Dream Team. He has had more recent success, winning Ligue 1 once again this season and being named the Ligue 1 Player of the Year. In his acceptance speech for the latter award however, he raised eyebrows with his comments about his future, fuelling speculation that he wanted to leave PSG.
The Parisian club would later release a statement refuting any claims that Mbappé was unhappy or that he wanted to leave. He is currently valued at £180m but PSG would likely demand a much higher fee if they were to part ways with him.
Bundesliga - Jadon Sancho
Jadon Sancho joined Dortmund from Manchester City in 2017 for a fee of £7m, and since then, he has become one of the most exciting talents in Europe. He has adapted extremely well at the German club, helping guide Der BVB to a title challenge and the quarter-finals of the Champions League.
His tally of 14 assists in Bundesliga was the joint-second highest tally among players in the top five European leagues.
The youngster has been at the centre of constant transfer speculation throughout the season, being strongly linked to Manchester United despite having played for rivals City. He is valued at approximately at £72m, but it would be likely for Dortmund to ask for a much higher transfer fee to sell Sancho considering his age and the impact he has made.
Serie A - Kalidou Koulibaly
The Senegal international has been one of the best defenders in Europe in recent years, and this season his performances have led to plenty of reports linking him with a move away from Napoli.
A commanding presence in the heart of defence, he has helped Napoli challenge Juventus at the top of Serie A in recent years.
Koulibaly has been strongly linked to a move to Manchester United for several months and the Red Devils have reportedly had a £96.4m bid rejected by Napoli, who insist that the defender is not for sale.
The 27-year-old's €150m release clause becomes active in 2020.
Premier League - Harry Kane
In spite of the fact that the likes of Eden Hazard and Paul Pogba have been linked with moves to Real Madrid this summer, the Premier League player that would command the highest transfer fee is undoubtedly Harry Kane.
Kane has become one of the best strikers in the world since he broke into the Tottenham first team. The England star has a magnificent scoring rate, with 164 goals in 252 appearances, and won back-to-back Premier League Golden Boots in 2016 and and 2017.
He has also managed to translate his fantastic goalscoring ability to the international stage, winning the 2018 World Cup Golden Boot as England reached the semi-finals - their best finish in a World Cup since 1990.
In recent months the 25-year-old has shown he is more than just a goalscorer, dropping off into midfield, linking up play and showing his excellent passing range by setting up others.
Kane has become Tottenham Hotspur's talisman over the past few years and will attract attention from the biggest teams in Europe, but with chairman Daniel Levy (who is know for being stubborn and shrewd in negotiations) at the helm, Spurs fans shouldn't worry too much about losing their star man. They have reportedly set a £312m price for Kane in order to ward off potential suitors.
La Liga - Lionel Messi
The Argentine magician is considered to be one of the greatest, if not the greatest, footballer of all time. He continues to break record after record and his domination of Spanish football seems to be even more pronounced following the departure of his greatest adversary Cristiano Ronaldo to Juventus.
Messi is a unique phenomenon in the sense that not only is he a magnificent goalscorer, but he is also a brilliant passer of the ball. His close control, dribbling, finishing, passing and vision have been his greatest attributes, as he continues to defy logic and play at such as high level into his 30s.
This season he has secured his 10th La Liga title and was the top goalscorer and assist provider simultaneously for the second consecutive season.
Of all the players on this list Messi would be the least likely to leave his current club. He joined Barcelona as a 13-year-old and his achievements have meant that he is revered by the Blaugrana supporters; a God-like figure who is likely to have a lifelong affiliation with the club.
Even at 32 years old Messi would still likely command one of the highest transfer fees in the history of the game in the extremely unlikely event that Barcelona decide to sell him.