McCoist said that the news was devastating and that his thoughts were with Ricksen and his family.
Celtic Football Club also passed on their best wishes to the former Rangers player.
Ricksen revealed earlier this week that he is suffering from amytrophic lateral sclerosis (ALS), which causes muscle weakness.
The 37-year-old, who made more than 180 appearances for Rangers between 2000 and 2006, made the announcement on a television show.
McCoist said everyone at the club wished him well, adding: "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 begin to imagine what he is going through at the moment."
Celtic said the thoughts of the club were with Ricksen and his family. "Everyone at Celtic passes on our best wishes to Fernando at this very difficult time."
A spokesman for the Motor Neurone Disease Scotland charity said it was saddened by the news of Ricksen's diagnosis.