The Blues midfielder, who joined the club in 2006 under recently reappointed boss Jose Mourinho, is unsure if he will remain at Stamford Bridge amid interest from Galatasaray
The Nigeria international is on an extended break after competing in the Confederations Cup but was non-committal when questioned about his Stamford Bridge future.
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"I have a four-year contract with Chelsea, but you know, in football you can never guess, one day you are here, the next day you might leave," he told Sky Sports.
Turkish club Galatasaray are reported to have shown interest in the 26-year-old who has made 182 league appearances for Chelsea without ever scoring a goal.
Chelsea have also been linked with other midfielders that could replace the Nigerian at Stamford Bridge, with Roma midfielder Daniele de Rossi and Vitesse youngster Marco van Ginkel both on the west London club's radar.