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.
Sweden shatter Italy's World Cup dream
The big news from the first leg is that Marco Verratti will miss the second contest after picking up a yellow card in Sweden. Immbobile beat Olsen with another but Andreas Granqvist got back for a decisive goal-line clearance.
European Union members ink landmark defense agreement
Ms Mogherini said that by coordinating their efforts, European countries would get better value for money in defence. This has led to unease by European allies that the USA was not committed to the alliance's mutual defense pact.
Idea Cellular reports Q2 net loss of Rs 1106.8 crore
That move comes as Idea and Vodafone's India business get set to merge , and begin selling off assets for debt repayment. A hotel employee clears a table after Vodafone Group and Idea Cellular news conference in Mumbai, India March 20, 2017.