#3 Lucas Digne to Barcelona
With the recent arrivals of Nuno Mendes and Achraf Hakimi, PSG have finally addressed the Achilles' heel of their otherwise star-studded squad. The lack of quality full-backs has always seemed to trouble the French giants in their pursuit of European glory. However, PSG only have themselves to blame as they voluntarily agreed to the sale of Lucas Digne back in 2016.
Currently regarded as one of the best left-backs in the Premier League, Digne was once an outcast in the PSG squad. Bought from Lille for €15 million in 2013, the French defender was scarcely used by the Parisians, making only 44 appearances in two seasons with the club.
After a decent loan spell with Roma, PSG happily offloaded him to Barcelona in 2016. Digne has since gone on to cement his place as one of the most invaluable assets at Everton, even captaining the side on multiple occasions. With the injury-prone Bernat and inexperienced Mendes as their primary left-backs at the moment, PSG would've definitely been a better side with Digne on their books.
#2 Christopher Nkunku to RB Leipzig
Christopher Nkunku is undoubtedly one of the most promising rising stars of the present time. His progression at RB Leipzig has been breathtaking, to say the least, with the 23-year-old Frenchman blossoming into a proficient attacking midfielder.
Witnessing his steady development has been a privilege for the footballing world, except probably PSG, who chose to sell him for a paltry fee of €13 million in 2019. Part of Les Parisiens' youth setup in his younger days, Nkunku is viewed as one of the great jewels of French football.
Nevertheless, this fact did not prevent PSG from selling their promising homegrown talent. Nkunku's recent hat-trick against a rampant Manchester City side proved that the Ligue 1 giants were reckless in letting him leave. According to various reports, PSG are now trying to buy him back for a significantly higher fee.
#1 Mike Maignan to Lille
A transfer that has since come back to haunt them, PSG's decision to sell Mike Maignan to French rivals Lille, recently deprived them of their 10th Ligue 1 title. Maignan was a pivotal cog in Christophe Galtier's inspiring Lille side of the 2020-21 season, which narrowly edged PSG to top spot in the league.
The Frenchman proved impenetrable in Les Dogues' title-winning campaign, conceding just 23 goals all season, all the while keeping a remarkable 21 clean sheets. He was subsequently chosen to be Gianluigi Donnarumma's heir at AC Milan following the Italian's free transfer to PSG.
The Ligue 1 giants arguably have the strongest goalkeeping duo in all of Europe in the form of Donnarumma and Keylor Navas. However, strengthening a direct title rival without even testing the talent at hand is equally inexcusable.
He failed to register even a single appearance for PSG in his two years being contracted to the senior squad. A perfect example of what could've been, the PSG's decision to sell him for a laughable fee of €1 million has utterly backfired.
Also read: 5 players Barcelona should have never sold