Celtic manager Neil Lennon has described Fernando Ricken's death as a "devastating" blow.
Rangers hero Ricksen lost his battle with motor neurone disease on Wednesday at the age of 43.
The Dutchman was one of the main figures at Ibrox during his spell the club.
Ricksen spent six trophy-laden seasons at Rangers after signing from AZ Alkmaar in the summer of 2000, going on to win two league titles, two Scottish Cups and three League Cups.
The former Dutch international, who picked up a dozen caps for his country, also won the PFA Scotland Player of the Year award alongside John Hartson in 2005
"It is tragic," Lennon said.
"I am very, very upset, for his family, obviously. And for someone I played against in many battles, at a time when both teams were very strong in Glasgow.
"In a very good era for Scottish football.
"For the Glasgow public to lose him at such a young age is devastating. He put up such an unbelievable fight, and as a player he got better and better during his time in Glasgow at Rangers.
"To the point where he became player of the year. He turned out to be an outstanding footballer and great competitor.
"He was emotional at the start of his career but he really matured into a very fine player.
"So our condolences go to his family and Glasgow Rangers as well. It is a huge loss.
"I have felt it myself, for someone who I played against for a long, long time."
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