England manager Gareth Southgate is wrestling with the biggest dilemma of his reign as he tries to plot a way to stop the "sensational" Kylian Mbappe in Saturday's World Cup quarter-final.
Southgate's hopes of leading England to a third successive semi-final at major tournaments hinge on finding a solution to a problem that has proved impossible for any team to solve in Qatar.
Just how do you subdue a player with Mbappe's lethal combination of electric pace, balletic skill and clinical finishing?
Australia, Denmark and Poland failed to come up with an appropriate answer as Mbappe scored in his three starts on route to the quarter-finals.
Poland defender Matty Cash summed up the conundrum posed by Mbappe after the Paris Saint-Germain forward's brilliant two goals in France's 3-1 last-16 victory on Sunday.
"I didn't know whether to drop off or go tight," Cash said. "When I went tight he just spun in behind. When he gets the ball, stops and moves, he's the quickest thing I've ever seen.
Exciting feature: Check out news exactly for YOU ➡️ find "Recommended for you" block and enjoy!
"He's a different level. Speed, movement, look at his finishing. He's got everything."
Four years after playing a key role in France's World Cup triumph in Russia, Mbappe is the tournament's most feared player.
The 23-year-old already has five goals in four games in Qatar, while his haul of nine career World Cup goals puts him level with Argentina's Lionel Messi and one ahead of Portugal star Cristiano Ronaldo.
Now it is Southgate's turn to sit the daunting Mbappe exam.
"Look, he is a world-class player who is always producing the moments when they are needed. That is what those top players do. That is the challenge we face," Southgate said.
So what will Southgate do to combat Mbappe's threat?
One answer would be to switch England's 4-3-3 formation to a 3-4-3 or 3-5-2 system, which would allow Kyle Walker to move from right back to supplement the central defence.
Southgate's concern is to avoid a situation in which the pacy Mbappe and Ousmane Dembele can run at defender Harry Maguire and exploit his lack of speed.
'Burning my legs'
Moving Walker would give Maguire help but it would also leave Southgate open to fresh claims he is a negative coach more concerned with stifling the opposition than letting his own stars express themselves.
Southgate was heavily criticised after his return to a 3-4-3 formation in the Euro 2020 final against Italy produced a tepid display that ended in a penalty shoot-out defeat.
Instead of changing his formation, Southgate may take inspiration from Walker's role in Manchester City's Champions League semi-final first-leg win over Mbappe's PSG last year.
City boss Pep Guardiola asked Walker to muzzle Mbappe from right-back and he responded with a disciplined display that kept the star from scoring.
"I can't think of another right-back in the world that I'd want to put up against him," former England defender Gary Neville said of Walker's chances of subduing Mbappe.
"Kyle will go closer to him, he has more pace than the Polish defenders. That's not to say Kyle will mark him out of the game. This is a sensational player, the new best player in the world."
As well as Walker winning his one-on-one duels with Mbappe, Neville believes it is essential to reduce his service from Olivier Giroud and Antoine Griezmann.
"If they can stop the service to Giroud and Griezmann in that central area, it means Mbappe's receiving far less dangerous passes," Neville said.
But no matter how much England plan for Mbappe, Cash knows from painful experience that nothing can truly prepare them to face such a unique talent.
"I spent the afternoon watching his clips, but I'm watching the videos while lying in bed. In real life, he's burning my legs, that's the difference, he said.