- Getty/Man Utd composite
Sanchez-Mkhitaryan: Man United-Arsenal
After almost joining Manchester City on deadline day in the summer of 2017 and then agreeing personal terms ahead of a seemingly inevitable January move to the Etihad, Alexis Sanchez stunned Pep Guardiola & Co. by moving to Old Trafford instead.
Manchester United’s offer to make the former Arsenal ace the best-paid player in the Premier League proved enough to turn the Chilean’s head, while the Gunners were happy to get a ready-made replacement in Henrikh Mkhitaryan. Ultimately, everybody seems to have got what they want... apart from City.
However, Guardiola's side enjoyed the last laugh, winning the Premier League title by a record-breaking 19 points from second-placed United, with Alexis struggling horribly to justify his lofty wage.
Barcelona won just about everything it was possible to win in 2009, but Pep Guardiola took the rather strange decision to remove a key component from that all-conquering team by sending Samuel Eto’o to San Siro as part of a €69.5 million (£56m) deal for Zlatan Ibrahimovic.
Eto’o, who had been bizarrely valued at just €20m, would win a second successive treble in 2010, but this time with the Nerazzurri rather than the Blaugrana, while Ibrahimovic lasted just one season at Camp Nou, after an infamous falling-out with Guardiola.
Indeed, as he later admitted in his autobiography, Zlatan once told his Catalan coach: "You have no balls!"
Having given Nemanja Matic just three senior appearances, Chelsea agreed to let a highly-rated midfielder head to Benfica in January 2011 as part of a €25m (£21m) deal for enigmatic Brazilian defender David Luiz.
After Jose Mourinho returned as manager, the Blues quickly moved to rectify their mistake, stumping up another €25m (£21m) to bring Matic back to west London in 2014.
Chelsea have also sold and re-signed Luiz since then, while moving Matic out once more to Manchester United for an estimated £40m in the summer of 2017, much to the bemusement of the club's fans.
Back in the summer of 2006, William Gallas wanted out of Chelsea – amid accusations that he had threatened to score own goals if he was not allowed to leave (something he later refuted) – and Ashley Cole was looking for an upgrade to his bank balance.
The solution to this problem? A swap deal which would also see Arsenal net £5m for their England international left-back.
Cole went on to win everything at Stamford Bridge, while Gallas threw the odd strop with the Gunners before crossing north London to join Tottenham.
Nunez-Owen: Liverpool-Real Madrid
As part of their ‘Galactico’ policy, Real Madrid swooped to land former Ballon d’Or winner Michael Owen from Liverpool in the summer of 2004.
Bit-part midfielder Antonio Nunez was sent in the opposite direction as part of an £8m transfer, but both players involved would spend just 12 months in their new surroundings before being sent packing.
In fairness, Owen did net 16 times for Madrid, including in a Clasico clash with Barcelona, but he struggled for regular starts and Nunez fared little better at Anfield as he was moved on to Celta Vigo after making just 18 Premier League appearances for the Reds.
Roberto Carlos-Zamorano: Real Madrid-Inter
Ivan Zamorano had helped Real to the La Liga title in 1995 with a 28-goal haul, but quickly slipped behind homegrown hero Raul in the pecking order. Inter offered him an escape route, with Roberto Carlos allowed to leave the San Siro after a frustrating year being used as a winger by Roy Hodgson.
Zamorano’s time at Inter is now best remembered for him donning 1+8 on the back of his shirt after losing the No.9 jersey to Ronaldo, while Carlos became a legendary left-back during 11 trophy-laden years at the Santiago Bernabeu – with his haul including three Champions Leagues and four La Liga titles.
Ambitious Inter assembled the world’s costliest strike-force when acquiring Christian Vieri to partner Brazilian superstar Ronaldo in 1999, with the Nerazzurri including midfielder Diego Simeone in a world-record €49m (£32m) deal for the Italy forward.
Vieri would net over 100 goals during his time at San Siro, but won just one Coppa Italia. Simeone, meanwhile, landed the Serie A title in his first season after being traded to Lazio – with a four-season stint in Rome proving to be the longest of his club career at any one team.
Gillespie-Cole: Newcastle-Man United
Netting 43 goals in just 58 Premier League appearances for Newcastle brought Andy Cole to the attention of Sir Alex Ferguson, and the Manchester United boss happily sanctioned the piecing together of a British-record £7m transfer package in January 1995.
The £1m-rated Gillespie was sent to Newcastle as part of the deal and, while he came close to helping the Magpies get back on the trophy trail, Cole offered greater value to the Red Devils as he became an iconic figure at Old Trafford with 121 goals and eight major honours during his six-year stay.
Deco was very much a man in demand in 2004 after helping Porto to Champions League glory under Jose Mourinho. Ricardo Quaresma had been in a similar position 12 months earlier, having shone in his native Portugal at Sporting, but he had struggled to make the desired impact at Barcelona.
A €15m (£13.4m) offer from Barca allowed Deco and Quaresma to trade places. While the latter fared well in Porto, the latter excelled at Camp Nou, with Deco playing a pivotal role in the Blaugrana winning their second Champions League, in 2006.
Coco-Seedorf: Inter-AC Milan
Inter do not have the best of records when it comes to trade deals down the years, with the Eto’o-Ibrahimovic deal about the only time that they have got things right.
Another example of a deal that they got very much wrong was pushed through in 2002, with the Nerazzurri doing business with fellow San Siro tenants AC Milan.
Inter took highly-rated, but easily distracted, left-back Coco, with Dutch midfielder Clarence Seedorf moving in the opposite direction. The former ended up retiring at the age of 30, while the latter conquered Italy and Europe on two occasions with the Rossoneri.
Exactly why Inter felt compelled to swap Fabio Cannavaro for Juventus goalkeeper Fabian Carini in 2004 remains shrouded in mystery.
It has even been claimed that former Bianconeri director Luciano Moggi told Cannavaro to feign injury in order to persuade the Nerazzurri to cut their losses on the centre-half, who had disappointed in the two seasons that followed his €23m transfer from Parma.
However, that story doesn't really explain why Inter felt Carini, who had spent the previous two seasons on loan at Standard Leige, was worth €10m – the same amount as Cannavaro. It remains one of the most bizarre valuations in football history and former president Massimo Moratti has never lived it down.
Of course, Cannavaro, who has always insisted that Inter "wanted Carini at all costs", went on to prove himself the best centre-half in the world, winning the World Cup in 2006 before leaving for Real Madrid after Juve were relegated from Serie A for their involvement in Calciopoli.
As for Carini, the Uruguayan made just four appearances for Inter before being allowed to join Murcia in 2007.