James Haswell, 48, died in hospital after falling ill with a suspected heart attack while watching the second half of his team's Clydesdale Bank Premier League game at Rugby Park on Sunday.
A statement from the club read: "Everyone at Kilmarnock Football Club extends their sincere condolences to the family and friends of the late James Haswell, who tragically passed away on Sunday 5th May after taking ill at Rugby Park during our match against Hibernian FC."
The statement added: "In particular, our thoughts and prayers are with his widow Aileen and daughters Nicola and Stephanie.
"Aged 48, Jim had been a life long supporter of Killie and a season ticket holder for many years. His love of Kilmarnock FC was deep rooted and it is a tragedy for all who share his passion for the club that we have lost a truly devoted supporter."
Mrs Haswell said: "Jim lived for Killie and his family. He only missed one game in 17 years. He was the biggest Killie fan you could know."
The club added that arrangements to mark Haswell's passing would be announced following discussions with his close family. The supporter was treated by paramedics and medical staff from both clubs before an ambulance drove pitchside to transfer him to nearby Crosshouse hospital.
The match was stopped by referee Kevin Clancy with the teams drawing 1-1 and both managers agreed the match should be abandoned out of respect.
It is the third such tragedy to hit Kilmarnock games in the past two seasons. In March 2012 the Ayrshire team's League Cup-winning celebrations were cut short by the death of midfielder Liam Kelly's father, Jack, who collapsed at Hampden immediately after the match.
A month later an Inverness fan collapsed and died midway through the second half of a game against Kilmarnock.
- Sports & Recreation
- Death & Funeral
- Kilmarnock Football Club