"I've been at Fulham a long time and now I think it is time I moved on," he told the London Evening Standard.
"It is not a decision I have taken lightly and I hope the fans understand, but I am a very ambitious player and I don't think Fulham have the necessary ambition any more since they sold Steve Finnan.
"The European Championships are coming up at the end of the season and I feel I would have a better opportunity of making them by moving to a bigger club.
"I have to think of myself. I want to improve as a player and this is a crossroads in my career. It has not been an overnight decision and I want the fans to know that."