IT can be hard for clubs outside of Europe's 'Big Five' leagues to compete with the wealthy elite elsewhere on the continent.
With the riches on offer to teams in England, Germany, Spain, Italy and France, clubs from lesser-monied leagues are forced to find value in the transfer market.
Celtic have done this well in recent years, raking in tens of millions for the likes of Moussa Dembele, Kieran Tierney and Virgil Van Dijk.
And with talented young players like Kristoffer Ajer and Odsonne Edouard on the books at Parkhead, the Scottish champions will be hoping that they can continue to make massive profits after picking up players relatively cheaply.
It's a transfer strategy that Rangers will need to copy if they're to catch up on Celtic financially, given the gulf in resources between the two rivals.
But if the Ibrox club are looking for a template to follow, there is an excellent example in Denmark.
Celtic's Europa League opponents FC Copenhagen have made a fortune in recent years by buying low and selling high, making just under £50m in profit off of just eight players.
Here are some of the best bits of business completed by the Danes in the last few years.
Denis Vavro
The Slovakian centre-half joined Copenhagen from MSK Zilina in his homeland for just £1.2 million in 2017 before leaving for Lazio last summer in a £9.5 million deal.
Robert Skov
The Danish right-winger was nothing short of a revelation for Copenhagen since joining from fellow Superliga outfit Silkeborg for £900k in January 2018. In his one full season in the Danish capital, Skov racked up 29 goals in 34 league games before sealing a move to Hoffenheim for £9 million last July.
Rubin Olsen
Another bargain recruit who has since moved on to bigger and better things since leaving the Parken Stadium, Olsen spent just two years with FC Copenhagen. The shot-stopper was snapped up from PAOK in Greece for around £600k before sealing a switch to Italian giants Roma in 2018 for just over £8 million.
Andreas Cornelius
You may remember the big Danish forward for his spell with Cardiff City in the Premier League in the 2013/14 campaign. The striker came through the youth ranks at Copenhagen before moving to the Welsh side for just shy of £8 million. The move didn't work out and he returned to Denmark's capital for just £3m a year later - but Cornelius then moved to Atalanta for another £4.5m a few years later.
Daniel Amartey
The Ghanaian centre-mid was brought to Copenhagen for a fee of £1.6 million in 2014 and just 18 months later, Amartey was on his way to England to join Leicester City in a £6m deal. He made three substitute appearances during the club's historic Premier League title win in 2015/16.
Federico Santander
The forward from Paraguay was not a cheap signing for Copenhagen after joining from Guarani in his homeland in a £2.8 million deal, but Santander proved to be a worthwhile investment three years after joining. After scoring 48 goals in 112 appearances for the Danes, a £5.8 million move to Italy's Bologna followed.
Jesse Joronen
Another goalkeeper that Copenhagen made a huge profit on. The Finnish keeper, who came through the ranks at Fulham, moved to Denmark's AC Horsens on a free transfer in 2017. A year later he sealed a switch to the capital for £800k before he joined Brescia in a £4.5 million deal last summer.
Bryan Oviedo
Another player who swapped Scandinavia for the Premier League, Costa Rican full-back Bryan Oviedo was brought to Copenhagen for just £400k in 2010. By 2012, he had impressed enough to convince Everton to part with £4 million to secure his signature. A spell at Sunderland followed before a return to Copenhagen on a free transfer last summer.
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