The city-state's football governing body withdrew its application for direct participation and FAS chief Zainudin Nordin explained in a letter to AFC President Mohamed Bin Hammam that Singapore would next compete at an "opportune time under the right circumstances in the near future."
Nordin said it would be difficult for the FAS to meet one of the revamped ACL's criteria that the top league of any national association should not contain any foreign teams.
"We concluded that due to our current lack of critical mass in key areas such as talent pool and resources, there is still a pressing need for us to continue having foreign teams participating in our league, to help address these gaps in our game and safeguard the sustainability of our league in football excellence, commercial and financial terms," the FAS President wrote.
Nordin stressed that the purpose of having foreign teams in the S-League was to inject "more excitement and competitiveness for our fans, expose our local teams and players to various styles of play, secure non-Singapore sponsors and attract more fans, especially those from the expatriate community residing and working in Singapore".
Of the 12 S-League clubs this season, three are foreign-based - French team Etoile FC, Chinese satellite club Beijing Guoan and Japan's Albirex Niigata.
Currently, the S-League champions qualify for the ACL via two play-offs.
Bin Hammam said he regretted the situation.
"We have taken on board the situation of the FAS. We hope they will consider seeking direct entry to the ACL soon," he told the AFC's website.
"It is hard to see Singapore out of AFC's professional football activities in spite of their great potential. We will work hard towards seeing them playing an active role in our professional football programmes in the future."
