Tweets sent by the ex-Republic of Ireland international's former clubs and team-mates suggest that he is battling a serious illness, with Tam McManus, Alex Bruce and Noel Hunt having mentioned cancer in their messages.
"Awful news about Liam Miller keep the fingers crossed that he somehow pulls through", McManus tweeted.
Miller started his professional career with Celtic before moving to United in the summer of 2004.
A short spell at Loftus Road was followed by stints at Hibernian, Australian clubs Perth Glory, Brisbane Roar and Melbourne City, home-town club Cork City and, most recently, Wilmington Hammerheads in America.
Miller was part of the Sunderland squad that won promotion to the Premier League in 2007 but moved again in 2009, this time to QPR.
Son scores 2 to give South Korea 2-1 win over Colombia
Things happen during a game like this. "Colombia have world-class players, and I was extremely disappointed to see such action". Colombia heads to China for another World Cup warm-up match on Tuesday, while South Korea hosts Serbia.
FBI Statistics Show Hate Crimes Rise in Minnesota in 2016
Some civil rights groups caution that the FBI's annual figures are artificially low because they rely on voluntary reporting. The rise marked the first time since 2004 that hate crime in the United States has increased two years in a row.