Bassong suffered from a knee complaint for the majority of last season, while Turner picked up a groin problem towards the end of the campaign.
"I think it was better for the ones left at home, Seb and Michael especially, to stay there. They wouldn't have taken part in any of the games over the 12 days," said assistant manager Colin Calderwood.
"You can't go straight into the work at too high an intensity. The first thing that we've got to do is make sure that we've got as many players training for 100% of the sessions that we've got – so that they don't miss a session."
Leon Barnett has also been kept behind to continue his rehabilitation.