Manchester United, Celtic and Brisbane Roar are among the clubs who extended well wishes to Miller after reports the former Republic of Ireland midfielder is battling cancer.
Miller, who won 21 international caps over a 16-year career, broke through at Celtic before he was lured to the Premier League by Alex Ferguson in 2004.
The 36-year-old, who played for Perth Glory, Melbourne City and the Roar, will begin chemotherapy this week, according to Scotland-based BBC pundit Tam McManus.
And former club Brisbane posted to Twitter to show their support for Miller.
"We send our thoughts and prayers to Championship winner Liam Miller and his family at this difficult time," they wrote.
Miller also had spells with the likes of Leeds United, Sunderland and Hibernian prior to stints in Ireland, the United States and in Australia.