Over the years West Ham fans have witnessed some emotional highs and even more crushing lows.

From the heartbreak of relegation to the second tier of English football in 2003 and 2011 to reaching the FA Cup final in 2006 and recording their best ever Premier League points total last season - the Hammers really have been there, seen it and done it in recent years.

And during all those ups and downs, the east London club have witnessed some great players go in and out of the doors - some via their famed academy, others via illegal transfer dealings - and you wonder what they might have achieved had they managed to keep hold of some of the best players to have pulled on the famous claret and blue in the Premier League era?

Here's a look at the five players West Ham should never have sold, where would they be now if this lot had stayed?

Rio Ferdinand

A product of West Ham's youth system, Ferdinand went on to become one the world's most highly rated defenders during his glistening career at both Leeds and Manchester United. While he was let go for a record fee of £18million, the Hammers will rue selling the ex-England international as he could have been the answer to their defensive woes over the past decade and a half.

Joe Cole

A fan favourite at Upton Park, Cole played with an enthusiasm and demeanour that made him not only brilliant to watch but also horrible to play against. England's 'Brazilian-esque' midfielder had it all: skill, a fine touch, vision and of course a thumping shot. He rejected a new contract with the club to move to Chelsea, and although he returned for a relatively successful spell in 2014, it was too little too late.

Jermain Defoe

Over the years, the Hammers have continually failed to sign a top class striker - with the exception of Carlos Tevez of course. They have signed countless forwards in an attempt to find themselves a 20-goal-a-season frontman but never realised they let one go years ago in the form of a young Jermain Defoe. He has now scored nearly 150 goals in the Premier League, and leaves West Ham fans wondering why it couldn't have been for them.

Frank Lampard

'Fat Frank' as he was known during his tenure at West Ham went on to be one of the greatest Premier League players of all time, scoring over 200 goals for Chelsea. At the time, many thought he was only in the West Ham squad because he was manager Harry Redknapp's nephew, but selling Lampard may have been the biggest mistake the club ever made as a man who could have been the cornerstone of their future turned out to be just that for someone else.

Javier Mascherano

He barely ever played for the Hammers after his controversial transfer which ended up costing West Ham over £5million in fines, and Mascherano moved to Liverpool only the season after. The Argentine was fantastic for the Merseyside club, and you can't help but think it the club had avoided the controversy surrounding his signature in the first place then they may have been able to keep hold of someone who turned out to be a world class player.