The Republic of Ireland international - who missed his country's 1-6 reverse to Germany at the weekend - sustained a hamstring pull against the Robins. Leicester went on to record a 2-0 home win without St Ledger.
St Ledger's injury, which sees him also ruled-out of the Boys in Green's match against the Faroe Islands tonight, leaves Ireland manager Giovanni Trapattoni with a defensive headache.
Meanwhile, young Foxes striker Tom Hopper has extended his loan deal at Bury and will remain in Lancashire until January. The 18-year-old has made seven starts for the Shakers and scored twice and will continue to be involved at Gigg Lane as Bury look for their first win of the season.