4. Diego Costa – valued at €84m (£66m) – Click the arrow for more – It was one of the most inevitable transfers of the summer, but it looks as though Chelsea managed to get Diego Costa for a bargain, given his sensational start to life at Stamford Bridge. The Brazilian-born Spaniards goals have seen his estimated worth rise to an eye-watering £66m. 10 10 3. Eden Hazard – valued at €99m (£77m) – Click the arrow for more – Without doubt one of the finest players in Europe, the sky is the limit for Eden Hazard. The Chelsea star has once again been the Blues shining light in an impressive campaign for the club thus far. As it stands, the Belgian is valued at around £77m. 9. Alexis Sanchez – valued at €61m (£47.7m) – Click the arrow for more – Given his hugely impressive return since joining Arsenal in the summer, the Gunners reported £35m fee for Alexis Sanchez looks like money well spent with the CIES now valuing him at around £47.7m. 10 2. Cristiano Ronaldo – valued at €133m (£104m) – Click the arrow for more – Once world footballs most expensive player (and in some reports, still considered to be), Cristiano Ronaldos £80m transfer fee looks like pocket change given the Portugueses current valuation. 10 7. Raheem Sterling – valued at €63m (£49m) – Click the arrow for more – Very much the darling of English football, there is a growing feeling that it is only a matter of time before Raheem Sterling moves for an exorbitant fee. If he were to move tomorrow, CIES predict that his valuation would be somewhere around the £49m mark. 10 10 10 10. Gareth Bale – valued at €60m (£47m)* – Click the arrow to see which players are considered the most valuable in the world! – He may have cost a world-record fee 18 months ago, but according to the CIES algorithm at least (see below for explanation), that valuation has plummeted. While Bale looks incredibly settled at Real Madrid, the Welshmans secondary role to the clubs biggest stars has impacted his goals and assists return compared to his final year at Tottenham. The football world was recently salivating at the prospect of a Lionel Messi meg-transfer, after it was reported that Argentine ace was threatening a move away from a Barcelona side gripped in civil war.Tongues started wagging over a prospective move to Chelsea, a rumour that appeared to disappear as quickly as it appeared, after talkSPORT revealed that it would cost around €200m to land the four-time world player of the year.Consequently, *the CIES Football Observatory have taken the opportunity to unveil their latest list of the 100 most valuable players in football.Using a tailor-made algorithm developed on the basis of over 1,500 transfer fees since 2009, they incorporate a number of variables such as player performances (matches played, goals scored, etc), age, position, contract duration and the level of competition said player competes in.Take a look at the countdown above to see who makes the top 10 and how much they are considered to be worth.To see the full list of the 100 most valuable players, click here. 8. Cesc Fabregas – valued at €62m (£48.5m) – Click the arrow for more – The ease with which Cesc Fabregas has slotted back into Premier League life has been hugely impressive and instantly asks questions as to why Arsene Wenger opted against re-signing the Spaniard. Arsenals loss has been Chelseas gain as Fabregas has excelled in the middle for the Blues. As such his valuation has sky-rocketed. 5. Paul Pogba – valued at €72m (£56m) – Click the arrow for more – Regarded as a future world footballer of the year, former Man United youngster Paul Pogbas stock continues to rise on a weekly basis. The French powerhouse was recently linked with a 70m move to Paris Saint-Germain, but according to CIES he is worth slightly more. 10 6. Sergio Aguero – valued at €65m (£51m) – Click the arrow for more – While they have managed to pull level with Chelsea in the league, there can be no disputing that Man City have missed their talisman Sergio Aguero in attack. The reigning champions spent a reported £38m in 2011 on the Argentine, an amount that has only increased since then. 10 10 1. Lionel Messi – valued at €200m (£172m) – He may not be the world player of the year, but Messi is ranked the most valuable footballer on the planet by the CIES calculations. The Argentine ace set the rumour mill into overdrive regarding a move to Chelsea. The Blues would have to splash out a princely sum, though!