Former Rangers captain Fernando Ricksen has been diagnosed with motor neurone disease.
Ricksen revealed on a live Dutch television programme on Wednesday night that he had the rare life-threatening condition.
The 37-year-old broke down in tears when he was asked by the presenter why he was talking so slowly.
Ricksen, struggling to control his emotions, asked the author of his book to explain that he had been diagnosed with Amyotrophic Lateral Sclerosis, which is also known as Lou Gehrig's disease.
ALS is the most common of the five motor neurone diseases with a life expectancy of less than five years for about half of those diagnosed with the condition.
It is a debilitating disease, characterised by rapidly progressive weakness, and muscle atrophy that leads to difficulty in speaking, swallowing and breathing.
Holding back the tears, Ricksen, who played for Rangers from 2000 to 2006, said: "The medical people have said my condition could worsen quickly. I do not know anymore."
Rangers manager Ally McCoist was shocked by the news and offered Ricksen all of the club's support.
"This is truly devasting news and the thoughts of everyone associated with Rangers Football Club are with Fernando," McCoist said on the club's website.
"We will of course support Fernando and his family in any way we can and there is no doubt football is put into perspective when you hear news like this.
"I have seen images of Fernando in today's media and my heart goes out to him and his family. I cannot begain to imagine what he is going through at the moment.
"He enjoyed a fantastic career at Rangers, notably captaining Rangers to the title in 2005 at Easter Road, and I know our fans will also show their support for him."
Ricksen began his career with Fortuna Sittard before moving on to AZ Alkmaar, and it was Dick Advocaat who brought him to Ibrox in 2000 for £3.75million.
The right-back was twice in trouble with the law during his spell in Glasgow for drink-related offences, but Advocaat trusted the player and signed him again for Zenit St Petersburg in 2006.
Advocaat is currently back at AZ for a second spell as manager, and told the club's website: "I always enjoyed working with Fernando. Of course, the stories about his escapades are known by many, but under me he was always a decent professional, and respectful.
"I have worked in a good and successful way with him at Rangers, Zenit and the Dutch national team. With Zenit, we won the Russian title and the UEFA Cup.
"It's terrible news Fernando is suffering ALS. It has deeply touched me. Also here at AZ, it touched people. He had three successful years here in Alkmaar.
"The club has good memories of him. I want to wish Fernando and his family and friends a lot of strength the coming period. Hopefully his winning spirit will give him the best."
Rangers' city rivals Celtic also issued a statement to express their sympathy.
The Hoops said: "The thoughts of everyone at Celtic are with Fernando Ricksen and his family following the news that he has been diagnosed with Motor Neurone Disease.
"Everyone at Celtic passes on our best wishes to Fernando at this very difficult time."
FIFA president Sepp Blatter was another to tweet, and posted: "Sending Fernando Ricksen strength today after his diagnosis with #ALS. I know about #MND through (former Italy striker) Stefano Borgonovo. Keep fighting Fernando."
Celtic legend Jimmy Johnstone died in 2006 after a five-year battle with MND aged 61.