Update 3.11pm: Republic of Ireland manager Martin O'Neill has sent his support to former Celtic player Liam Miller amid reports he is battling pancreatic cancer.
The 36-year-old midfielder is said to be undergoing treatment and news of his plight has been greeted with shock by acquaintances within football.
Speaking at his pre-match press conference ahead of Ireland's World Cup play-off second-leg clash with Denmark, the former Bhoys boss said: "I gave Liam his debut at Celtic. He played wonderfully well in a Champions League game one evening, he was absolutely outstanding.
"The news - we heard about it just recently, we didn't know how bad it was - and obviously all thoughts go out to him and his family. I think he's got three children as well.
"He's a very young man, 36 years of age. It puts things in perspective."
There was support too from fellow Corkman David Meyler, who said the 21-times-capped Ireland international is in the thoughts of the current squad.
Meyler said: "We've obviously heard the news. We're unsure of all the details, but our thoughts go to his family. We are thinking of him and we hope he can pull through and he's strong anyway.
"That's from the whole team and everyone."
Update 1.33pm: Celtic and Manchester United have expressed their support for former midfielder Liam Miller after reports that the 36-year-old is battling pancreatic cancer.
The former Republic of Ireland player is reportedly receiving treatment in the United States, where he last played for Wilmington Hammerheads.
Celtic wrote on their official Twitter account: "The thoughts and prayers of everyone at Celtic Football Club are with Liam Miller and his family at this time."
Miller made his professional debut for Celtic in 2000 after coming through the youth ranks at Parkhead and helped them win the Scottish Premier League title in 2004.
He then moved south to United on a free transfer, making 22 appearances under Sir Alex Ferguson in two seasons - which included a spell on loan at Leeds - before joining Sunderland in 2006.
Miller was part of the Black Cats' squad that won promotion to the Premier League in 2007 but he was on the move again in 2009, this time to QPR.
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.
Many of his former clubs and colleagues have publicly expressed their support for Miller through social media.
John Hartson, who played alongside Miller at Celtic, tweeted: "My thoughts are with Liam miller and his family this morning. Hope he can get through this difficult time of his life."
My thoughts are with Liam miller and his family this morning. Hope he can get through this difficult time of his life.— John Hartson (@JohnHartson10) November 13, 2017
Jacob Burns, the former Leeds and Australia midfielder who is now head of football at Perth Glory, tweeted: "In shock! Thoughts and prayers are with my old team Mate and friend Liam Miller as he and his beautiful family fight through this battle!"
In shock! Thoughts and prayers are with my old team Mate and friend Liam Miller as he and his beautiful family fight through this battle!❤️— jacob burns (@JacobBurns07) November 13, 2017
Miller won 21 caps for the Republic between 2004 and 2009, and current Ireland international David Meyler said the squad are thinking about their compatriot.
The Hull midfielder told a press conference on Monday: "Obviously we heard the news, we're unsure about the details, but our thoughts go out to his family and we're just thinking about him and we just hope he can pull through and he's strong. That's from the whole team and everyone."
Earlier: The good wishes and support of the sporting world in Cork, Ireland and beyond, are with former Ireland player Liam Miller who is battling cancer, writes Gráinne McGuinness.
The 36-year-old, who played with Celtic and Manchester United as well as a season with Cork City in 2015, is home in Cork to undergo treatment for the illness.
In recent seasons, he has been playing with Wilmington Hammerheads in the United States, where he lives with his wife and family. It is understood he had been treated there in recent weeks before making the decision to return home. His parents live in the family home in Ovens.
Pat Malone, chairman of Éire Óg where Liam played as a child, said the whole community was rallying in support of the family.
“There is a lot of shock in the community,” he said. “The family would be very well known in the area, they have lived here all their lives.
“He played with us and with soccer clubs in the area. Soccer was always his first love but at underage he played a lot with us, as did his brothers.”
A midfielder, Liam began his career with Celtic and spent two seasons with Manchester United as well as periods with Leeds United, Sunderland and QPR. He also played at international level from U19 up, earning 20 senior caps with the Republic of Ireland between 2004 and 2009.
Many former teammates have sent their good wishes to the midfielder.
John Hartson, who played with Liam at Celtic, said: “My thoughts are with Liam Miller and his family this morning. I hope he can get through this difficult time of his life.”
A number of former Ireland internationals have expressed their sorrow at news of his illness.
Fellow Ireland international Ian Harte said: “Very sad news about one of my old teammates Liam Miller, thinking of him and his family at this very difficult time.”
“Such sad news about my old roommate Liam Miller,” said former Leeds and Reading player Noel Hunt. “Pray to God he pulls through this battle with cancer, my thoughts and prayers are with him and his family.”
Former Celtic player Darren O’Dea added: “All my thoughts and love with Liam Miller and his family.”
This story originally appeared in the Evening Echo.