The Lions have slid down from 154th at the start of the year, with Vietnam remaining the best in Southeast Asia at 133rd, and Japan as the region's kingpins at 32nd
Singapore remained at 165th in the latest Fifa world rankings released on June 6, while arch rivals Malaysia moved up two spots to 159th position.
Singapore started the year on 154th before sliding down four places to 158th in February, and continued their slide over the next two months before settling down on their current position in May.
Although the British Overseas Territory of Bermuda did not play any matches in the past months, they miraculously moved three spots up to 161st, while the Solomon Islands dropped a spot below Singapore to 166th.
Japan is still Asia’s best ranking team despite dropping two places to 32nd while South Korea and Australia remain the next two best teams in Asia in 40th and 47th respectively.
Vietnam retained their tag as the highest-ranking Southeast Asian nation in 133rd although they went down a spot from the previous month, while Thailand stayed in 142nd, two positions above the Philippines.
The other Southeast Asian countries such as Laos and Indonesia remained in the same position as the previous month in 168th and 170th respectively, while Myanmar moved up three spots to 155th.
Brunei Darussalam, Timor Leste and Cambodia made slight improvements as all three countries moved up a spot.
The Sultanate and the region's youngest nation share the 185th position while Cambodia sits above the Pacific islands of Vanuatu and Tonga in 189th.