It's little wonder the January transfer window was so quiet. 

Some of the biggest clubs in Europe are strapped for cash right now, with Barcelona's ongoing financial crisis just one example. 

However, football's economic doom-mongering could still pave the way for a lot more action this summer as sides look to cash in on some of their biggest names to raise funds.

There are also a handful of cases - Lionel Messi and Sergio Aguero being among the most sensational possible coups - of massive contracts being run down. 

Yet clubs will only be able to make serious money back off their outgoing superstars if they perform well in the coming months.

That's not been the case for Tottenham's Dele Alli, or Real Madrid's Eden Hazard. The decline of the two playmakers, who were at their peak in the Premier League just a couple of years ago, has been sad to see.

They aren't the only ones to have gone downhill, mind you. Transfermarkt have listed the 20 players in world football whose market value has decreased the most since June. 

In some cases, like Messi's, his new valuation of £72 million is a reflection of the fact he has just six months left on his current deal. But for others, it's a worrying indictment of their career trajectory since the summer. 

Let's take a look: 

20. Matteo Guendouzi - £22.5m (-13.95m)

19. Milot Rashica - £10.8m (-14.4m)

18. Harry Maguire - £36m - (-£14.4m)

17. Pierre-Emerick Aubameyang - £36m (-£14.4m) 

16. Marco Reus - £13.5m (-£15.3m) 

15. Kepa Arrizabalaga - £13.5m (-£-15.3m) 

14. Sergio Aguero - £31.5m (-£15.3m) 

13. Jadon Sancho - £90m (-£15.3m) 

12. Dani Parejo - £9m (-£16.2m) 

11. Sergio Busquets - £9m (-£16.2m) 

10. Raheem Sterling - £99m (-£16.2m) 

9. Isco - £18m (-£18m)

8. Leroy Sane - £54m (-£18m) 

7. N'Golo Kante - £54m (-£18m) 

6. Samuel Umtiti - £9m (-£19.8m) 

5. Dele Alli - £34.2m (-£23.4m)

4. Eden Hazard - £45m (-£27m) 

3. Lionel Messi - £72m (-£28.8m)

2. Christian Eriksen - £31.5m (-£29.7m)

1. Antoine Griezmann - £54m (-£32.4m)

Maguire has made a number of errors for United and he's now worth just £36m. 

Aubameyang might sympathise, given the season he is having at Arsenal, scoring just five Premier League goals and doing little to justify his new contract. 

Tottenham, meanwhile, would probably be lucky to get north of £30m for Alli when Mourinho has made it so apparent that he isn't part of his plans. The same goes for his former teammate Eriksen, who has flopped at Inter Milan and was even linked with a return to north London last month. 

Curiously, the biggest decrease of all is attached to Griezmann, who has impressed for Barcelona in recent weeks. If the Frenchman keeps putting in such impressive performances for the Blaugrana, his value will surely rocket back up again soon.