Cusack, named vice-captain last month, had just started her sixth season with the Blades in the Women’s Championship and was the longest-serving player in their current squad.
A statement on the club’s official website read: “Sheffield United Football Club is devastated to report the sad news of the passing of Maddy Cusack.
“Maddy, a women’s team player since 2019 and marketing executive for the Football Club, passed away on Wednesday.
“A respected player, Maddy, 27, last season reached the milestone of 100 appearances for Sheffield United Women.
“Additionally, she was a valued colleague in the offices at Bramall Lane, moving over from the Sheffield United Community Foundation to the club in 2021 to help market all areas of the Blades.”
Cusack joined the Blades halfway through their first campaign in the women’s second tier in January 2019 and last season became the first woman to reach 100 appearances for the club.
The former England youth international signed a new contract extension with the Blades in July.
United’s chief executive officer Stephen Bettis said: “This is heart-breaking news for everyone at Bramall Lane.
“Maddy had a unique position of being part of a number of teams at Sheffield United and was popular with everyone that she came into contact with.
“Her personality and professionalism made her a credit to her family – she will be sadly missed.
“While taking in the news and moving forward, the club will offer as much support as possible to Maddy’s family, friends and colleagues.”
The Blades said talks over “suitable tributes and celebrating Maddy’s life” will continue privately, adding: “The club and Maddy’s family would appreciate a period of privacy and will not comment further at this sad time.”
