When you're called 'Sweden's new Zlatan Ibrahimovic' on the occasion of your 17th birthday, you might expect to be at one of Europe's biggest clubs when you're 20. So...how about Alexander Isak then?

Was the hype too much? With the legendary striker coming into his twilight years, was the pressure placed on Isak's shoulders a burden too great to bear at such a young age?

Only time will tell, but Real Sociedad's stunning 4-3 win over Real Madrid in the Copa del Rey was another indicator that this 20-year-old striker is a star in the making. ​Borussia Dortmund just weren't willing to wait for him to shine.

His two goals on Thursday night were not just instinctive runs to the back post followed by simple tap-ins, they were supremely composed finishes that demonstrated the vast array technique in his repertoire. 

On his unfavoured left foot, he adjusted well to fire a perfectly crafted volley across Alphonse Areola to put his side two goals in front, before showcasing his devastating finishing with a rifled effort that flew into the top corner at the goalkeeper's near post.

Two finishes of the highest order to form a brace that shouldn't come as a major surprise. He's been doing this for a while

Starting out at AIK in his native Sweden, he scored 13 goals in his debut season having forced his way into the first team at just 16 years old. In April 2016, he became the youngest goalscorer for the club in the Swedish top flight, 166 days short of his 17th birthday. 

Goals kept coming and Dortmund took note, bringing him to the ​Bundesliga for a deal worth around £7.8m, with the rumours being that Isak even turned down ​Madrid in favour of the German side.

He was given a place in the reserve team initially, with a view to bedding him into senior side in due course. Injury stopped that happening sooner, but he would go on to feature in matchday squads with the first team sporadically throughout the 2017/18 campaign. 

He was never handed a regular run with the senior side though, making just five top flight outings - more often than not as a late substitute. This did little to aid his development, and while a return to the reserve team for the first half of the following campaign was fruitful, Dortmund saw it best to loan him out to Willem II for the remainder of the season.

As an example of what a regular spell in the starting lineup can do, Isak bagged 14 goals in 18 appearances for the club, firing the Dutch side to a top ten finish in the Eredivisie. In doing so, he became the first foreign-born player in Eredivisie history to score 12 goals in his first 12 appearances. He didn't let his head drop when farmed out, and instead showed Dortmund what they were missing. Talk about an impact.

Alexander Isak

Isak isn't your average number nine, certainly not the 'poacher' type, anyway. Instead, what drew the gazes of so many sides across the continent was his excellent skill on the ball. Isak boasts technical ability that is not normally seen in strikers his age, where he is happy to pick the ball up from deep and start attacks himself before bursting into areas in the box where he can collect the ball and have a pop at goal.

He's also equally adept at running the channels and taking defenders on, something that played a key role in him having a successful stint in the Netherlands. 

Even still, when playing in a side like Dortmund who see plenty of the ball, his finishing in and around the box is both accurate and lethal. It's already been mentioned that he favours his right foot, but he's not one-footed enough that shifting the ball onto his right in order to get a shot off is a necessity.

Speaking of Dortmund, his playing style resembles that of Erling Braut Haaland. He's roughly the same height, boasts similar pace and is lethal in front of goal.  

Alexander Isak

So when the news came that Dortmund had accepted a bid from Real Sociedad for £5.8m last summer, there was surprise all round that the club had not only let him go, but done so for less than they originally paid for him.

Moving to Spain would ensure regular football, but why Dortmund weren't willing to wait and see Isak flourish into the player he was hyped up to be is a question only the club themselves can answer. Maybe they knew they were getting Haaland all along?

Either way, it's a decision that has benefited La Real massively this term. His goals against Zinedine Zidane's side were his 12th and 13th of the campaign, in just 27 appearances. An understanding has been forged with Martin Ødegaard, and the pair regularly link up to devastating effect.

The fact he's capable of finding the back of the net in sides that don't boast world-class talent is another telling sign of his quality, as his movement and raw talent allow him to find the space where he can be most dangerous. It's clear he has an eye for goal, so it's just a shame he couldn't showcase that in a team featuring Marco Reus and Jadon Sancho. One can only imagine how many goals he'd have this season if that was the case.

Still only 20 years old, Isak is paving the way for a successful and prolific career. While Real Sociedad are performing well in ​La Liga, it's only a matter of time before a move to one of Europe's more established sides is on the cards.

Dortmund could have been the beneficiaries. They just didn't have the patience to see him blossom.

For more from Ross Kennerley, follow him on Twitter!