William Jay Grierson (; born 27 April 1998) is a professional footballer who plays for Hong Kong First Division side Eastern District.
Born in Sai Ying Pun, Hong Kong to a British father and a Chinese Filipino mother, William began his footballing journey in Hong Kong with the TSW Pegasus youth side in the local grassroots division. He soon completed his tertiary education at the Ateneo de Manila University whilst representing the youth national team of the Philippines.
Grierson began his career with PFL side United City, striking his first professional deal aged 23. William made his debut for the side in a 2-0 loss to J League side Kawasaki Frontale in the 2021 Asian Champions League group stage. He departed the club ahead of the 2023 PFL season.
Grierson joined Eastern District on a free, ending his 1 year football hiatus.