Justice Christopher, who starred for Nigeria against England at the 2002 World Cup, has died suddenly at the age of 40.
Christopher collapsed at the hotel he owned in Jos in Central Nigeria, and his body has been taken to the Plateau Specialists hospital, where an autopsy is expected to be carried out this week.
He reportedly played a social game of football on Tuesday afternoon and was found dead on Wednesday morning, with no official cause of death given yet.
The Nigeria Football Federation (NFF) said in a statement it was "devastated" to learn of Christopher's death.
Christopher captained Nigeria's Under-20 team in 2001 and the midfielder went on to earn 11 senior caps for the Super Eagles.
He played at the 2002 Africa Cup of Nations and in all three group matches at the World Cup in Japan and South Korea later that year, where the West Africans finished bottom of a group containing Sweden, England and Argentina.
His Nigeria team-mate, and the country's first man to win 100 caps, Joseph Yobo also paid tribute to his "close friend".
"My family and I are deeply saddened by the awful news that my close friend Christopher has passed away. Thoughts and prayers go out to his family," the Super Eagles assistant coach said.
"A very gentle man that we shared some wonderful memories with throughout our international career. He will be missed by so many people and I honestly can't get over the shock."
Christopher established himself on the domestic scene with Katsina United, Sharks and Bendel Insurance, before moving to Belgian club Royal Antwerp in 2001.
A stint with Bulgarian side Levski Sofia followed, before adding spells at Swedish outfit Trelleborg, Russian side Alania Vladikavkaz and Danish club Herfolge Boldklub.