Celtic and Manchester United have expressed support for their former midfielder Liam Miller after it emerged that the 36-year-old has pancreatic cancer. The former Republic of Ireland player, who won 21 caps for the Republic between 2004 and 2009, has reportedly received treatment in the US, where he last played for Wilmington Hammerheads.

Celtic wrote on Twitter: “The thoughts and prayers of everyone at Celtic Football Club are with Liam Miller and his family at this time.” Manchester United said: “The thoughts of everyone at Manchester United go out to Liam Miller and his loved ones at this difficult time.” Another of his former clubs, Sunderland, also tweeted in support. The Republic of Ireland manager Martin O’Neill added that the news “puts things in perspective”.

“I gave him his debut at Celtic,” O’Neill said. “He did wonderfully well in a Champions League game one evening, he was absolutely outstanding. We heard about the news recently but we didn’t know how bad it was. All thoughts go out to him and his family. I think he has three children as well. Such a young man.”

The Ireland midfielder David Meyler said: “Thoughts go out to him and his family, from the whole team. We’re thinking about him and we hope he can pull through.”

Miller’s former Ireland team-mate Noel Hunt wrote on Twitter: “Such sad news about my old room-mate Liam Miller, Pray to God he pulls through this battle with cancer, my thoughts and prayers are with him and his family.”

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 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 Sunderland squad that won promotion to the Premier League in 2007 but moved again in 2009, this time to QPR. A short spell at Loftus Road was followed by stints at Hibernian, the Australian clubs Perth Glory, Brisbane Roar and Melbourne City, his 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.”

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!”

Meyler said the current Ireland squad are thinking about their compatriot. “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.”