Speaking on Twitter, Kasabian's dad Simon Newton Smith said this morning: "Kas passed peacefully in his sleep."
Sheffield United fan, Kasabian, from Parson Cross, was diagnosed with cancer when he was two years old but developed inoperable brain tumours last year.
Following the announcement Sheffield United have proposed a minute's applause during the eighth minute of today's game to mark inspirational Kasabian's eight years of life.
A spokesman for the club said on Twitter: "Sorry to learn that young Blade Kasabian has passed away. We propose a minute’s applause on 8mins for the 8yo at today’s game #twitterblades"
Last month Billy Sharp dedicated United's win against Chesterfield and the goal he scored to little Kas, as part of the #1LastSmile4Kasabian campaign on Twitter.
The campaign was started in a bid to bring birthday celebrations for Kasabian, who was due to turn nine later this month, forwards.
Sharp and Blades teammate Chris Basham visited Kasabian last month, and Sharp enlisted the help of former Southampton teammate Adam Lallana to make one of Kasabian's dreams come true - to receive a video message from England skipper Wayne Rooney.
Rooney sent Kasabian his signed shirt from last month's Scotland game, and Sharp - named man of the match as United beat Chesterfield - dedicated the victory to Kasabian in his live post match interview with Sky Sports.
When Kasabian was told his cancer had returned this June he responded by starting a massive fundraising campaign to build a new clinic at Sheffield Children’s Hospital.
The selfless youngster even tried to give his wish from the Make-A-Wish Foundation away to another youngster who he thought deserved it.