Sydney coach John Longmire faces a month-long selection headache, as the AFL's reigning premiers determine just who of their young guns are playing on borrowed time.

Longmire revealed on Tuesday that injured trio Adam Goodes (knee), Lewis Jetta (shin) and Sam Reid (quad) - all walk-up starters when fit - are 3-4 weeks away from senior selection.

At best, they'll return for the Swans' round-22 clash with Geelong but, realistically, it's more likely to be Hawthorn six days later or week one of the finals.

Whenever it comes, Longmire will have to make room and it won't be easy.

Incumbents Jed Lamb, Brandon Jack and Tom Mitchell are the least experienced in the team, but all have impressed for the second-placed Swans after making debuts earlier this season.