McQueen, 40, died from asphyxiation and hanging, according to coroner's official Lynda Martindill. The contents of the note were not released, but the results of a full autopsy are expected to be released in a few months.
Police suspect there was no malice, and the inquest to formally rule McQueen's death as a suicide has been adjourned until April 28, the AP reported.
McQueen was found dead in his apartment on Thursday. Days prior, the British designer expressed his grief about the death of his mother on Twitter, posting messages about his "awful week" and saying he had to "somehow pull myself together and finish."
Celebrities including Rihanna, Lady Gaga and Sarah Jessica Parker often wore McQueen's pieces.