Stalls handler Stephen Yarborough has died after suffering serious injuries in an incident before the fourth race at Haydock on Friday.
Yarborough was in his role as team leader at the Merseyside course when he was involved in an accident with the starting stalls before the running of the fourth race, which was scheduled for 3.30pm.
His employers RaceTech said in a statement: "Following a tragic accident today our dear friend and colleague Stephen Yarborough sadly passed away following serious injuries incurred in his role of Team Leader of the Starting Stalls at Haydock Park Racecourse."
John Bozza, chief executive at RaceTech, expressed his shock and sympathy, saying: "Our thoughts are very much with Stephen's family, close friends and his colleagues at this very sad time.
"Stephen was an experienced and popular member of the team; he will be hugely missed by everyone. We are doing all we can to support Stephen's family and the investigation at this stage."
Yarborough had been flown to Whiston Hospital by air ambulance and admitted to intensive care.
The remainder of the meeting was abandoned, with the police arriving to the scene.
The stewards held an inquiry, at which they interviewed the race starters and clerk of the course Kirkland Tellwright, who represented the Racecourse Executive.
Tellwright informed the stewards the executive had taken the decision to abandon the rest of the card as "the police had been informed of the accident and were due to arrive at the track to conduct their inquiries".
The Saturday evening meeting scheduled for Haydock - due to feature Culture Club in a concert after racing - appeared set to go ahead.
A post on the track's Twitter feed read: "Following the abandonment of racing today, currently Saturday's fixture will go ahead as planned."
Nick Rust, chief executive of the British Horseracing Authority, expressed his shock at the news.
"This is a tragic incident and we are all shocked and saddened," he said in a statement.
"Stalls handlers carry out a brave and important job each day looking after the safety of the horses and riders and we are grateful for their work.
"British racing will come together in grief at this incident - we are one family and today we have lost one of our own. Our condolences and sympathies are with his Stephen's family and friends."