A host of Europe's biggest clubs are thought to be lining up a move for the winger this summer, with Dortmund increasingly resigned to losing him.
It will take a significant sum to prise him away from the Bundesliga outfit, though, and that fact was underlined earlier this month when the CIES Football Observatory named him the most valuable footballer to have been born since 2000.
The stats show exactly why, but how does he compare to some of the other great players in recent times?
Unsurprisingly, all five of these players were first-team regulars by the time they turned 20, although some had gathered more experience than others at this stage.
Sancho has made 90 first-team appearances for Borussia Dortmund since joining from Manchester City, but that tally only puts him fourth out of the five on our list of comparisons.
Mbappe leads the way having played 122 senior club games before his 20th birthday, while Cristiano Ronaldo had made 104 appearances and Neymar exactly 100.
Somewhat surprisingly, Messi was significantly behind the rest of the pack at the age of 20, making just 70 Barcelona appearances during his teenage years.
Messi and Ronaldo will both go down among the greatest goalscorers the game has ever seen, with Messi boasting 627 and Ronaldo 626 at club level in their illustrious careers so far - a combined total of 1253.
However, the legendary duo trailed the rest of the pack at this stage of their careers, when Ronaldo had only 16 goals to his name and Messi had 26.
Sancho finds himself in the middle of the pack in this category having netted 31 times in his 90 games, some 15 behind Neymar, whose goalscoring exploits at Santos saw him register 46 times before his 20th birthday.
Mbappe once again leads the way, though, boasting an incredible 63 senior goals during his teenage years at a stunning average of a goal every 1.94 games.
Neymar's average is the next best at a goal every 2.17 games, while Sancho slips behind Messi when it comes to a goals-per-game ratio with one every 2.9 compared to one every 2.7 for the Argentine.
Ronaldo, meanwhile, left himself with a lot of making up to do having averaged a goal every 6.5 games during his teenage years.
Messi is not just the goalscoring king of football at the moment, he is also one of the most creative players to have played the game and boasts the most assists in La Liga history.
However, the six-time Ballon d'Or winner registered only 12 assists before his 20th birthday - four fewer than Ronaldo and 13 behind Neymar's pace at the same stage.
The other two are some way clear of their fellow superstars, though, with Mbappe creating 41 goals for his teammates as a teenager and Sancho just about pipping him in this category with 42.
That gives the Englishman a superb ratio of an assist every 2.14 games, compared to one every 2.98 games for Mbappe.
Neymar, meanwhile, averaged an assist every four games, Messi one every 5.8 games and Ronaldo one every 6.5 games before they turned 20.
While Sancho compares favourably to some of his most notable predecessors at club level, he still has some experience to make up on the international scene.
The former Manchester City player has won 11 caps for England, scoring twice and registering four assists, whereas Mbappe sits at the top of this category with 28 international appearances, 10 goals and seven assists by the time he was 20.
Ronaldo, meanwhile, had scored seven goals and created eight more in 18 games for Portugal, while Neymar had scored eight times and registered two assists in 15 outings for Brazil.
Sancho is closest to Messi in terms of experience as this stage, with the Argentine having scored four goals and chalked up four assists in 14 international games as a teenager.
Ronaldo is some way clear in terms of goal contributions, having a direct hand in one every 1.2 games, with Neymar next on 1.5, Mbappe third on 1.65, Messi fourth on 1.75 and Sancho trailing the rest with a goal or assist every 1.83 games for England.
All in all, Sancho compares very well to some of the greats of recent years; taking all of his senior matches at both club and international level into account, the newly-turned 20-year-old has directly contributed to 79 goals in just 101 games - an average of one every 1.28 outings.
Of the five players chosen, only Mbappe fared better during his teenage years, and even then only narrowly with 121 goal contributions from 150 matches - an average of one every 1.21 games.
The two youngest players on this list have made more progress in the early stages of their careers than the standard-bearers who came before them, with Ronaldo and Messi - arguably the two greatest of all time - trailing the rest.
Ronaldo had directly contributed to just 47 goals in 122 games by the time he was 20 - or one every 2.6 matches - while Messi had a hand in 46 goals from 84 games, an average of one every 1.83 appearances.
Neymar sits in the middle of the pack overall, meanwhile, having registered 81 goal involvements in 115 games at an average of one every 1.42 games.