As Celta Vigo romped to a stunning upset over Real Madrid in the Copa Del Rey this week, one name in particular would have made for difficult reading for Liverpool fans: Iago Aspas, who nabbed a goal and an assist in the Bernabeu boil-over. 

Aspas is one of those rare players who struggled, at times to comical effect, at one club - in this case Liverpool - before embarking on a meteoric rise at his next destination: football's 'ones that got away'. Here are six of the very best. 

Iago Aspas

Thrust into the Liverpool limelight, Aspas of limited English and low profile, was stuck in a queue of attacking talent that included Luis Suarez, Philippe Coutinho, Raheem Sterling and Daniel Sturridge. He ran out 14 times in the famous red strip, with nothing to show for it but a big, fat bagle. And this:

Shipped off to Sevilla on loan, then ultimately re-signed by Celta Vigo, Aspas set about becoming one of the best players in LaLiga – which is no easy feat at a club outside the top echelon. Ok, Liverpool fans. Look away. This season Aspas is fourth in the scoring list with 11 goals from 17 league matches, just behind Lionel Messi, Cristiano Ronaldo and Suarez. His three assists is second only to Suarez and his 57 percent shot accuracy is equal best in the competition and well ahead of Ronaldo’s 49 percent.

Earlier this week he carved up Real Madrid at the Bernabeu – with a goal and an assist - in Celta’s Copa Del Rey win.

Proving he can cut it on English soil, the 29 year-old scored on his international debut - against England at Wembley in November - to further dispel doubts about his talent. Liverpool fans are justified in wondering what might have been had the club signed him in the far more settled Klopp era.

Gerrard Pique

Pique was the right player at the wrong time for Manchester United – the gangly 17 year-old stuck behind a conga line of talented defenders, headed by Rio Ferdinand and Nemanja Vidic in their prime. He made cameo appearances in a four-year stint at the club from 2004-2008, but leapt at the chance to join Barcelona in 2009 under its then-new manager Pep Guardiola.

Guardiola would later describe Pique as his best ever signing, the smooth play-making centre back drawing comparisons to Franz Beckenbauer as he ascended to football’s top echelon of players.

Pique, who looks back fondly at his time in Manchester, had shown glimpses of the talent that would come to define his status as one of the best defenders in the world, as a fledgling first-teamer under Sir Alex Ferguson.

While that club has famously struggled to find a central pairing post Vidic and Ferdinand, Pique and his new team-mates embarked on a merry romp through football’s record books, amassing almost every trophy on offer in the club game along the way, multiple times.  It all makes for rather somber reading for United fans.

Pierre-Emerick Aubameyang

Take heart, at least you’re not a long suffering AC Milan fan – a sentence inconceivable during the late nineties.

Milan was still basking in the glow of its 2006-2007 UEFA Champions League win when a raw, athletic striker from Gabon named Aubameyang joined the youth team. 

He gave a glimpse of his prodigious speed and talent by scoring against every opponent in the Champions Youth Cup that year, finishing as the tournament’s top scorer with seven goals from six games.

That wasn’t enough to convince the club of his first team potential, despite Milan's dwindling stocks up front. Aubameyang embarked on a magical mystery loan tour of the French first division, being picked up by Dijon, Lille, Monaco and St Etienne, while still on the books at the Rossoneri.

St Etienne signed him permanently in 2011-2012. He rewarded the club with a league-best 16 goals from 36 matches. He scored 19 the next season and was snaffled up by Borussia Dortmund to replace Robert Lewandowski.

These days he is considered one of the best strikers in Europe and is regularly linked with the likes of Real Madrid and Barcelona. As Milan has lurched from one inauspicious season to the next, its former player has established himself among the best attackers in the game. All the club had to do was give him a chance.

Kevin De Bruyne

Chelsea fans may well still cringe at the sight of ‘KDB’ in a Manchester City shirt. The Blues snaffled up the prodigious talent from Belgian club Genk in 2012, before loaning him out to Werder Bremen. A string of eye-catching performances in the Bundesliga prompted incoming manager Jose Mourinho to sign off on  bringing the play-maker back to Stamford Bridge in 2013.

De Bruyne struggled for game time at Chelsea amid conflicting reports of a falling out with the manager. Mourinho says De Bruyne didn’t enjoy training under him and it was with a heavy heart that he gave the thumbs up for the player to be sold to Wolfsburg in January 2014.

The football stratosphere beckoned and De Bruyne was only too happy to oblige, blossoming into one of the game’s finest attacking midfielders in his second Bundesliga stint. It was enough to convince Manchester City to shell out $A94 million for him in 2015. He has been among the club’s most consistent players since then, scoring himself a spot on the shortlist for the Ballon d’or in 2015. Jaded Chelsea fans haven't let their old manager, Mourinho, forget the De Bruyne decision, ridiculing him about it whenever his Manchester United outfit turns up at the Bridge.

Riyad Mahrez

By his lofty standards, the Algerian is enduring something of a difficult second season at Leicester. But it’s not a patch on his anonymous last season at Le Havre.

That’s Le Havre, of French Ligue 2 fame - the club where Mahrez struggled for game-time until then-Foxes manager Nigel Pearson offered him a lifeline.  

That gamble proved to be one of the signings of last season, as Mahrez danced his way to a shock Premier League title alongside unheralded buddies Jamie Vardy and Ngolo Kante. Indeed, either of those players could command a place on this list. Though neither could boast as rapid a transformation as the Algerian, whose fleet-footed form had him linked with cashed-up suitors the football world over, from Barcelona to PSG and Juventus.

Mahrez’s mind may be justifiably elsewhere this season, as he contemplates a move away from the club he helped etch into sporting folklore.

Diego Costa

Atletico Madrid was on the brink of offloading Diego Costa to Turkish Super Lig club Besiktas  in 2011 when the brutish striker ruptured his anterior cruciate ligament and the deal was off.

That injury proved to be a turning point in a hitherto nomadic career plagued by disciplinary incidents and inconsistency. After being signed and offloaded by Portugal’s Braga in 2006 with 13 games and no goals to his name, Costa joined Atletico Madrid, where he went out on loan to three Segunda Division clubs with mixed results at each.

He was signed by Valladolid in 2009, before returning to Atleti the following year and being loaned to Rayo Vallecano.  It was this loan stint, Coasta’s fifth in six years, where he gave the strongest indication of his talent, netting 10 goals in 16 matches.

Despite that haul, Atleti was eager to offload him to Turkey when the injury struck.  Over the next three years Costa found the balance between aggression and talent, emerging into one of the most lethal and sought-after strikers in the game.

He secured a big money move to Chelsea, made his Spain debut and consolidated his reputation as a tough, technically proficient striker with an insatiable desire to score and win. How Braga would love to have invested a little more time into him all those years ago.