A statement from the Parkhead side read: “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.”
And former Celt, Stiliyan Petrov, in remission after being diagnosed with leukaemia in 2012, said on Twitter: “I’m saddened to hear the news about Fernando Ricksen! My thoughts and prayers are with you and your family at this difficult time! God Bless.”
The 37-year-old told a Dutch TV chat show, where he was promoting a new autobiography, that he was diagnosed with the incurable condition Motor Neurone Disease a month ago.
Ricksen told the programme on the Nederland 3 channel: "I find it difficult to talk because I've got ALS [Motor Neurone Disease]."
Ricksen's biographer, Vincent de Vries, said that he was planning to speak to doctors today about the diagnosis.
Mr de Vries said: "Fernando has been diagnosed with a muscle disease, ALS. He's going to hospital tomorrow to discuss the diagnosis in detail with the hospital and the doctors."
Motor neurone diseases [MNDs] are a group of progressive neurological disorders that destroy the cells that control essential voluntary muscle activity.
This includes speaking, walking, breathing, and swallowing.
They are more common in men, particularly those over the age of 40, than women.
Amyotrophic lateral sclerosis (ALS) affects the upper and lower motor neurons and can affect the arms, legs, or facial muscles.
There is no cure or standard treatment for MND.
How long someone may live with the disease depends on the type they have been diagnosed with and the age it started.
Ricksen signed for Rangers in 2000 for a fee of £3.75million from AZ Alkmaar, making 182 appearance and was briefly captain, before heading to Zenit St Petersburg in 2007. He was part of the 2004-05 Scottish Premier League title winning side which also won the League Cup.