Max George said he will be undergoing heart surgery "way quicker than the doctors first thought".
The Wanted singer said he had been diagnosed with a "2:1 block in my heart", a condition where the heart beats more slowly or with an abnormal rhythm, after he was admitted to hospital on Wednesday.
After a scan on Monday, George said "we don't have too much time to wait", explaining that his heart rate has remained low and he will need surgery sooner than expected.
"Unfortunately my heart rate hasn't picked up at all in almost a week," the 36-year-old said on Instagram.
"Because of this, we don't have too much time to wait so it looks like I'm going to be in surgery way quicker than the doctors first thought. I may even be home for Christmas!
"Still a pretty scary time right now and the last few nights have been really rough, but I wanted to say that I'm absolutely humbled by all your messages of support.
"Both people I know and those I don't. It's given me a much needed boost and my family have been overwhelmed with support, which means more to me than anything."
A heart block is caused by a problem with the electrical pulses controlling the heartbeat, according to the NHS website.
Manchester-born George said a full CT scan is "not something I'd choose to do again", as he shared a series of images with wires attached to his chest.
Tom Parker, who rose to fame in The Wanted alongside George, died in 2022 at the age of 33 after being diagnosed with an inoperable brain tumour.
The boyband formed in 2009 and achieved hits including UK number ones All Time Low in 2010 and Glad You Came in 2011.
George also appeared in US musical series Glee and competed on Strictly Come Dancing in 2020, where he met former EastEnders star Maisie Smith, who is now his girlfriend.
Smith, 23, and George said their friendship turned romantic in 2022.
