Albirex Niigata (S) Ong started his professional football career by signing for the Singapore Premier League side,
Albirex Niigata (S) on 16 December 2019. On 18 October 2020, Ong made his professional debut with
Albirex Niigata (S) against Young Lions by coming on as a substitution for Ryosuke Nagasawa in the 86th minute, playing till the end of the match. Ong won his first-ever major trophy in professional football by winning the
2020 Singapore Premier League with
Albirex Niigata (S). Tampines Rovers Yu En signed with Tampines Rovers at the start of the
2022 Singapore Premier League season.
South Korea stints In December 2022, it was announced that Yu En with
Fathullah Rahmat will train with
K-League 1 sides,
Incheon United U-18 and
Suwon Samsung Bluewings U-18 team and senior squad of
K-League 2 club,
Cheonan City from 26 December 2022 to 5 January 2023.
2025–26: Loan to Young Lions Yu En was loaned to
Young Lions ahead of the
2025–26 season. ==International career==