The 26-year-old has starred in west London since arriving from Lyon for £24.4 million in 2005, making 102 league appearances for the Blues - in various outfield positions - and netting 11 goals.
Essien's return from injury last season coincided with the club's dramatic up-turn in form, helping Guus Hiddink's side achieve FA Cup success at Wembley and scoring a stunning volley against Barcelona in the Champions League semi-finals.
However, 'The Bison' could now be lining up for the Catalans in 2009/10, after the player's agent, Fabian Piveteau, revealed that while Essien is happy at Chelsea, he would be interested in a switch to Spain should either Barca or big-spending Real Madrid come calling.
"Some clubs are interested in Michael," he told Kick Off Ghana.
"He likes Chelsea very much, but football is football and if Real Madrid, Barcelona or some other club make an offer, he needs to sit down and discuss what is best for him."
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