Toby, from Osmandthorpe, had captured the hearts of supporters and residents across the city after being diagnosed with stage four neuroblastoma in 2017.
Leeds United owner Andrea Radrizzani and players have expressed their condolences tonight (Sunday), after a statement issued by his family said the young Whites fan had now died.
Despite undergoing groundbreaking treatment, made possible following a Â£200,000 fundraising campaign backed Leeds United, doctors confirmed that Toby's cancer returned last year months after he was given the all-clear.
In a message on Twitter, Leeds United said: "Heartbroken. The memories will live forever. We love you Toby x"
The club's owner, Mr Radrizzani, added:" RIP little angel Toby. I keep in my heart sweet and beautiful moments at Elland Road together. We love you angel. My prayers for you and your strong parents."
And Liam Cooper, who previously carried the youngster onto the pitch at Elland Road, said: "Heartbroken to hear that my little mate has peacefully passed.. I will forever cherish the moments we spent together. Heaven has gained a beautiful angel.
"Your smile will live with me forever. Sleep tight little man I love you."