Prime League

The Prime League was the reserve and youth team soccer league of Singapore's S.League. Teams involved in the league are primarily made up of youth players from the S.League clubs. The Prime League was founded in 1997. S.League clubs are required to participate, and clubs who do not play at S.League level are also eligible to enter. In 2018, the Prime League was abolished, with the National Football League (NFL) installed as the second-tier competition.

Participation rules
All S.League teams had to register a minimum of 15 and a maximum of 20 players for the Prime League. Clubs not participating in the S. League had to register a minimum of 15 and a maximum of 25 players. The teams should maintain the minimum required number of players throughout the season. Each club was allowed to register 1 foreign player for their Prime League teams. The foreign players must have been aged between 18 and 21 at the point of registration and are not eligible to play in the S.League.

An S.League player who had played in his club's most recent S.League match was not eligible to play in the club's next Prime League match.

Prime League sides were also allowed to take part in the FA Cup competition.