The move is the latest blow to the embattled label, which which was taken over last year by the private equity firm Terra Firma and which has been losing top artists Paul McCartney and Radiohead.
Coldplay and Gorillaz are also believed to be thinking about jumping ship.
"The question is, 'Should Robbie Williams deliver the new album he is due to release to EMI?'" said Tim Clark, the singer's manager. "We have to say the answer is 'No.' We have no idea how EMI will market and promote the album. They do not have anyone in the digital sphere capable of doing the job required. All we know is they are going to decimate their staff."
NME's Paul Stokes called Williams' strategy "a massive blow for EMI" and noted, "The label used to have a Rolls-Royce roster of names on its books, but they are slowly but surely leaving."
Although EMI declined to comment, an industry insider told the Telegraph the label could sue Williams for "an absolutely enormous amount" if he fails to fulfill his contract.