During a league match against his former club, the Warriors, at the Singapore National Stadium, Zainol made a string of saves to keep his former side at bay in a 2–0 victory, gaining him the nickname "King of Kallang".
During a league match against Lion City Sailors on 18 October 2020, Zainol was sent off after performing a reckless tackle on Arshad Shamim, conceding a penalty at the same time which back-up goalkeeper Hairul Syirhan could not keep out.
Zainol citing that football wasn't a secured job for him due to contract negotiations and decided to sign on with the Singapore Civil Defence Force.
Following the arrival of Zaiful Nizam from Geylang International, Zainol was yet again relegated back to the bench but still made appearances for the club's Under-21 Center of Excellence squad.
On 3 January 2024, Albirex Niigata Singapore announced that he has signed with the club and will serve as a back up goalkeeper to his former Warriors teammate, Hassan Sunny.