Some of the best players in world football have been let go by their clubs and, when looking back, their former sides may well regret their departures. 

Here are five of the biggest player departure regrets: 

5. Daniel Sturridge - Chelsea to Liverpool

Sturridge always had potential as a footballer from when he was playing for England U16s. He moved from Manchester City from Chelsea and was expected to do great things at the club. He started well however fell out of favour at Stamford Bridge - even a very successful loan move to Bolton couldn't force him into the side.

His January 2013 move to Liverpool for £12m now seems like an absolute bargain. He's unleashed his true potential and has notched himself 18 goals at his time at Anfield. The 24-year-old has also saw himself gain a vital part within the England side.

4. Jaap Stam - Manchester United to Lazio

Sir Alex Ferguson openly admitted that he regretted letting powerful centre-back Jaap Stam depart Old Trafford.

Although, he was bound to miss half a dozen games, Stam was solid at the back. After his departure, United struggled and didn't defend their title. They finished third, 10 points behind winners Arsenal. They also faced problems at the back, losing nine games and conceding 45 goals all season - 15 more than second Liverpool.

3. Paul Pogba - Manchester United to Juventus

Ferguson let a young, inexperienced Pogba go when his contract ran out 2012. I'd love to know what he didn't see in the French international.

Antonio Conte signed him for free with Juventus and what a bargain it has turned to be. The youngster has turned into one of the best attacking midfielder's in the world today. That's a region that United have really struggled in of late. 

Pogba is becoming one of footballs greatest stars with sides like Chelsea and Real Madrid chasing his signature. As Red Devils fans if they'd have him back over Fellaini - I'm sure you can guess the answer

2. Gerard Pique - Manchester United to Barcelona

Ferguson made some cracking signings when in charge at Old Trafford, but he also made some terrible mistakes. 

Pique was at United for four years, and was never given a chance in the side. He spent a year on loan at Real Zaragoza and that still wasn't enough to impress.

However Pep Guardiola saw Pique's class and snapped him up for €5m, which seemed generous at the time.

Treble that and that may not even be a fair price for the player has excelled into. He's been inspirational at the heart of the Barcelona defence and formed a formidable partnership with Carles Puyol.

1. Cristiano Ronaldo - Sporting Lisbon to Manchester United

Although he was just 18 and £12M was a very good price for Ronaldo, what he went on to do in Manchester was legendary.

Lisbon could have kept Ronaldo for an extra two seasons and double the price they paid for him. United paid £25M for Wayne Rooney and although Rooney's world class, he's no Ronaldo.

Ronaldo helped United win the Champions League and numerous league titles. Imagine what Lisbon could have done if they kept hold of him for a bit longer.

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