Ricksen made the announcement on Wednesday after being diagnosed with the incurable condition two weeks ago.
The 37-year-old worked under Advocaat at both Rangers and Zenit St Petersburg as well as with Holland while the defender also spent three years with AZ until 2000.
Advocaat admitted he had been shocked by the news and told reporters: "The terrible news that Fernando suffers from motor neurone disease has deeply touched me.
"Even at AZ it has hit us hard.
"He was here in Alkmaar for three successful years, the club has good memories of him.
"On behalf of myself and AZ I want to wish Fernando and those around him much strength in the near future.
Ricksen got himself into a number of scrapes during his career but Advocaat added: "I have always worked extremely well with Fernando Ricksen.
"Of course the stories about his escapades are known to many but he has always been a good professional under me. The excesses I learned about later .
"Fernando was always respectful to me.
"I had him at both Glasgow Rangers and Zenit St Petersburg and the Dutch national team and successfully worked with him.
"With Zenit we became champions together and we won the UEFA Cup ."
Ricksen had told interviewers in his homeland: "I am very sick. I am fighting for my life."
But declaring his determination to fight for his health for the sake of his wife Veronica and their daughter Isabella, he added: "I have feared for a couple of months I was in trouble - it is very hard to take.
"Inside me there is a fighting spirit, there always has been. I will fight this - I know it will be difficult but I will battle all the way. I have Veronica and Isabella - they are my second life and I have to try."
Ricksen is understood to have amyotrophic lateral sclerosis, a form of the rare degenerative condition that attacks the central nervous system.
As the illness progresses, sufferers find it increasingly difficult to walk, speak, swallow and breathe.
Ricksen signed for Rangers in a deal worth around £4million in 2000 and left to sign for Russian side Zenit St Petersburg six years later after falling out with then Ibrox boss Paul Le Guen.
He won two Scottish Premier League titles, two Scottish Cups and three League Cups during his six-year spell with the Light Blues and was also named joint SPFA Player of the Year in 2004-05 alongside Celtic striker John Hartson.