Jurgen Klopp did not need any time to think. The best young player he had ever worked with? There was no doubt about it. The answer came to him immediately.
"Mario Gotze," the Liverpool boss enthused earlier this month. "He was unbelievable!"
Gotze had always been good, of course. His talent at a young age was undeniable, breaking into the Borussia Dortmund team as a teenager under Klopp in 2009-10 before helping BVB win the Bundesliga title the following season, scoring eight goals in all competitions and turning provider for 11 more.
It is now easy to forget that the Memmingen-born attacker is just 25, such was his precocious talent. He arrived fully formed on the scene, with incredible dribbling skill and an ability to pick out a pass that made him unstoppable wherever he was asked to play across the attack in support of the striker.
Unlike Robert Lewandowski, who developed into a superstar under Klopp's guidance, Gotze already was a star, long before he turned 20. He has won a trophy or individual award every year since being named the Golden Player at the European Under-17 Championship in 2009.
His successes at Dortmund earned him a move to Bayern Munich, becoming the most expensive German player ever at the time.
Although his spell at Bayern saw him become a squad player and suffer criticism for a lack of effort, Gotze still won a league title in each of his three seasons in Bavaria and, most importantly, scored the winner for Germany in the World Cup final in 2014.
A return to Signal Iduna Park last season should have seen him back to his best in the familiar surroundings of his boyhood club, but he was laid low with a muscular illness and was forced to take time away from the game.
Some feared that this could spell the end of one of Germany's brightest talents but, in August, Gotze started his first game in seven months and provided an assist in a 3-0 defeat of Wolfsburg.
While Gotze was away, Germany won the Confederations Cup with a team of young and eager footballers, but Dortmund felt his absence as they finished third in the Bundesliga behind Bayern and upstarts RB Leipzig.
Gotze's return was a welcome sign for new BVB boss Peter Bosz, with the former Ajax manager putting him straight back into the team to help create opportunities for Pierre-Emerick Aubameyang. After four assists in his first 11 games of the season, Gotze felt like his old self again.
"I am finally back at 100 percent," he told Sport Bild. "I have a really good feeling out there on the pitch. I realise that I want to take on responsibility and that I can actually do so as well. The team gives me the trust."
He also made his international return for Germany, coming off the bench to set up the stoppage time equaliser in the 2-2 draw with France. A full 90 minutes for Dortmund followed, and despite a 2-1 defeat to Stuttgart, his performance proved that the 25-year-old is fit and ready to once again shine on the club game's grandest stage.
Dortmund host Tottenham in the Champions League on Tuesday and nothing less than victory will suffice if BVB are to keep their faint hopes of reaching the last 16 alive.
However, Bosz can, at least, call upon a rejuvenated player who was once compared to Lionel Messi. Super Mario is getting back to his best, and when he gets there, no-one will stop him.