There are not many footballers - far less 18-year-old Scottish ones - who turn down a European superpower when they come calling.

A key factor in his decision was that the Italian side wanted him as an immediate part of their first-team squad, after just 33 senior games for the Tynecastle outfit.

Having surpassed that total for his new club by nailing down a regular first-team place in the Serie A team, the 19-year-old has earned a first Scotland call-up for Thursday's friendly against Poland.

How has Hickey become "one of the standout young players in Europe"? BBC Sport Scotland asked the man who gave him his debut, Craig Levein, as well as others he made an impression on at Hearts.

'No worries about throwing him in'

Hickey started his football journey at Hearts then joined Celtic aged 12 and spent four years playing in their academy teams before deciding he had a better chance of first-team minutes elsewhere.

That prompted a move back to Tynecastle in 2018. And, in the penultimate Scottish Premiership game of the 2018-19 season, the 16-year-old was given his senior debut in a 2-1 defeat at Aberdeen.

He started the following match, a 2-1 loss at Celtic, then a week later made history when the sides met again, becoming the youngest player to start a Scottish Cup final in the modern era as Hearts were beaten 2-1 at Hampden.

"I had absolutely no worries about putting him in against Aberdeen," says Levein. "He played because he was training so well. I watched all the youth games and he steadily improved from the period where he came back to us from Celtic.

"I had a little bit of doubt about throwing him in at Celtic Park but he proved he was more than capable of doing the job."

Hickey's Hampden appearance aged 16 against Celtic made him the youngest player to start a Scottish Cup final in the modern era

Taking Serie A by storm

Graeme Souness. Joe Jordan. Denis Law. It's quite the exclusive club Hickey has joined in making Serie A history.

When the teenager thumped home a 20-yard strike in a 2-2 draw with Genoa in September, he became just the fourth Scot to score in Italy's top flight.

No-one had done it since Souness 35 years previously. "It's crazy" is how Hickey described his feat, adding: "To be with names like Souness and Joe Jordan is a great achievement for myself. I'm really proud."

Three further league goals have followed for Hickey, who has thrived as a marauding left-back under coach Sinisa Mihajlovic.

The Scot did his due diligence in weighing up where his career would be best served. He visited Bologna's facilities, as well as Bayern's, and cited the "family feel" as one of the reasons for choosing the Italian side.

Another aspect to tip the balance was Bologna's pledge to include him in their first-team squad, while Bayern - European champions at the time - would have put him in their second team, which plays in the German third tier.

Hickey has certainly made the decision look a good one; after 12 appearances in an injury-interrupted debut season, he has been a near ever-present this term, starting the large majority of Bologna's games.

Plenty of young footballers have an ego to match their talent, but Levein believes Hickey's temperament will help him stay grounded.

"He never speaks, he just smiles," Levein says. "He's a bit shy but it helped him going into big matches, because he never seems to get flustered about anything."

Versatility enhances Scotland prospects

Hickey's form simply couldn't be ignored. Steve Clarke admitted as much last week after handing the teenager a first senior call-up by saying: "If you look at the way Aaron has played for Bologna over the course of the season, he is one of the stand-out young players in European football."

There is little doubt his call-up is merited, even if bypassing the traditional age-group trajectory has not been without controversy.

Having been capped by Scotland Under-17s, Hickey did not play for Scot Gemmill's Under-21s after pulling out of squads three times. His most recent withdrawal was last November and the reason - a need to rest - raised questions over his commitment.

However, he has now been elevated into Clarke's set-up, and finds himself in a stacked queue for the left-back berth, the natural position for Andy Robertson, Kieran Tierney and Greg Taylor.

That's where Hickey's versatility could be handy. Despite spending the majority of his short senior career at left-back, he has also featured on the opposite flank.

What's more, when he returned to Hearts, it was as a central midfielder.

"He's got really good defensive qualities but I don't know if he'll end up being a full-back, he might end up going back into midfield," Levein adds.

"He could be a fantastic holding midfielder with his great awareness of danger and his ability to get out of tight situations with the ball at his feet."

Former Hearts captain and striker Steven Naismith, now the club's football development manager, was also impressed with Hickey's game intelligence.

"His understanding of the game, without thinking about it, is very good," he said.

"All the small, quick decisions that need to be made on a pitch, Aaron predominantly makes them right and on top of that he's got a good attitude."

Hearts manager Robbie Neilson, meanwhile, says Hickey's on-field maturity shines through.

"He's like a 24 or 25-year-old in a teenager's body," he says. "He understands the game already. He has massive potential. I've been really impressed with him. He's very mature for his age, he's composed, has good physique, ticks all the boxes."

Former Hearts boss Craig Levein gave Hickey his Hearts debut