On March 10, 2015, an exciting young forward from Gelsenkirchen's famed Knappenschmiede youth academy announced himself to the football world. The stage could not have been bigger: a Champions League knockout tie against Real Madrid at the Santiago Bernabeu.

The game was already tied at 1-1 on 29 minutes when Leroy Sané entered the arena as a substitute. But within an hour of play he had piqued the interest of coaches, scouts and owners around Europe.

His frizzy locks tied back to keep from flying into his eyes, Sané eased into the match and by the second half was purring along. He glided through the game like he belonged in the same breath as the goal scorers that day – Cristiano Ronaldo, Karim Benzema and Klaas-Jan Huntelaar.

Yet Sané, who had only just turned 19, had just 101 minutes of first-team football under his belt. It was his Champions League debut.

Receiving the ball on the edge of the box, he turned and within two touches had curled the ball past World Cup winner Iker Casillas to level the game up at 3-3. A driving run from within his own half then led to Huntelaar giving Schalke a shock 4-3 lead.

The Royal Blues were one agonizing goal away from a historic two-legged victory against the competition's most fabled side. But their season dovetailed after that match as they failed to requalify for the Champions League.

Since then, Sané's and Schalke's fortunes have gone down different routes. The player swapped the Bundesliga for the Premier League and developed into one of the world's most promising forwards. Schalke, meanwhile, have endured a topsy-turvy time under new management.

- Read more: Leroy Sané is crucial to Germany's brave new world

Diverging paths

Moving to the Citizens in the summer of 2016 for €50 million, Sané boasted raw potential but still lacked that polished finish. Many thought that his move arrived a year too early for the then 20-year-old, who had made 57 first-team appearances while scoring 13 goals and assisting eight.

But his progression under the tutelage of Pep Guardiola has been incredible. In 118 matches, Sané has slotted home 35 goals and assisted on 41. Last season he was named the Premier League's Young Player of the Year and has continued his progression into 2019.

A tally of 12 goals and 14 assists has him sitting behind just Sergio Aguero and Raheem Sterling as City's most potent attacking force this season. Sané will be warmly welcomed back to Schalke – his parents still live in the Ruhr region and his brother Sidi plays for the club's U16s – but they'd rather it was in different circumstances.

"We're looking forward to seeing Leroy again," said sporting director Christian Heidel. "But he's bringing a team with him that's one of the favorites in the Champions League. There's hardly a bigger challenge."

Schalke fans can only watch with envious eyes as yet another youth product passes by. Under Heidel, whose first piece of business as sporting director was to sell Sané, the club's recruitment drive has been underwhelming. High-profile players followed Sané out the door, including Thilo Kehrer, Naldo, Benedikt Höwedes, Sead Kolasinac, Leon Goretzka, and Max Meyer (the latter three on free transfers) and their replacements have failed to fire.

Numerous positions are in need of reinforcement. Despite a second-placed finish under coach Domenico Tedesco last season, they've gone backwards in this campaign, currently lying in 14th.

Sané's return with a world-class outfit will only remind Schalke of how far they are from turning themselves into regular Champions League competitors.

Bigger fish to fry

For Sané, the move from Schalke has been an undoubted success. But despite his time with Manchester City, he hasn't yet had another chance to impress against a true European giant such as Real Madrid. He didn't feature against Barcelona in 2016 and couldn't halt City's capitulation against Liverpool last season.

Victory over Schalke could provide him another chance to impress against a big-hitter such as the Spanish giants or Italian champions Juventus in the Champions League quarterfinals.

It's the stage Sané was born to grace, ever since that first foray in the competition almost four years ago. If he does put his old club to the sword on Wednesday, it will be another step on his path to the pinnacle of the game. 

As for Schalke, they can only grasp hold of the fact that he was, at one stage, one of their own.