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The pop singer was previously a regular on the city's nightclub circuit, but has been shunning his old associates and spending more time at home with girlfriend Ayda Field.
"I haven't seen Robbie for ages," one pal told the Daily Star. "The last time I did, he was sporting an awful Robinson Crusoe style beard and looked as if he hadn't had a bath in days."
Another source added: "We all know he's an incredibly talented showman when he's on the stage and on the hip US club scene. But perhaps it's just that Robbie is so in love with Ayda he hasn't got time for clubs any more."
Williams decided to move across the pond in 2006 following criticism of his Rudebox album.
He has since revealed that he enjoys being able to live a normal life in LA, where he is relatively unknown.
