Ex-England striker Chris Sutton said: "All thoughts and prayers go out to my old teammate Liam Miller tonight".
He tweeted: "Awful news about Liam Miller keep the fingers crossed that he somehow pulls through".
The Welshman said: "My thoughts are with Liam miller and his family this morning".
The 36-year-old, who had spells at Celtic, Manchester United and Sunderland, has received widespread support from some of the famous names he would have played with, both at club and global level.
The former Republic of Ireland player has reportedly received treatment in the United States, where he last played for Wilmington Hammerheads. "Obviously all thoughts go out to him and his family, I think he has three kids, he's a young man at 36 years of age and it puts things in perspective anyway".
Republic of Ireland worldwide David Meyler said the squad are thinking about their compatriot ahead of their play-off match against Denmark.
Several Irish internationals, as well as the wider footballing community, used social media to wish their former teammate well and express support for him as he battles the illness.
"The thoughts of everyone at Manchester United go out to Liam Miller and is loved ones at this hard time" a tweet from United read.
His former Hibs team-mate McManus also claimed that he is undergoing chemotherapy. Thoughts go out to him and his family.
This story originally appeared in the Evening Echo.