LONDON — As heartbroken friends and fans mourned George Michael online and at his homes across Britain on Monday, questions swirled about the health and final weeks of the electrifying pop singer before his death on Christmas Day at the age of 53.

Once an indisputable sex symbol of the peak-MTV era, Mr. Michael appeared overweight and nearly unrecognizable in photographs, reportedly from September, that the website TMZ published on Monday. News media attention also fell on a 2015 tabloid interview with a relative claiming that Mr. Michael was abusing drugs and putting his life at risk. And after years of arrests related to drug use, as well as confessional interviews and health scares, the singer had largely retreated from the public eye, while his creative output had all but ceased.

[ Why George Michael mattered | Read the obituary ]

Paul Gambaccini, a radio and television presenter who had known Mr. Michael since youth and represented him during a 2011 tour, said in an interview that he was not surprised by the singer’s death because Mr. Michael was “not completely well” and had a “close brush with death” five years ago when he nearly succumbed to a bout of pneumonia. Doctors had to perform a tracheotomy.

Police officials, who had announced that Mr. Michael died in “unexplained but not suspicious” circumstances at his home in Goring-on-Thames, England, could not be reached for further details on Monday because of Boxing Day. The singer’s manager, Michael Lippman, on Monday declined to elaborate on his statement that Mr. Michael had died of heart failure, “in bed, lying peacefully.” Forensic experts said an autopsy report could be ready in a couple of days.