Gregan is now expected to be named in the 30-strong touring party which will play Tests against France in Marseille (November 5), England at Twickenham (November 12), Ireland at Lansdowne Road (November 19) and Wales in Cardiff (November 26).
Australia coach Eddie Jones, who will reduce the squad to 30 by October 10, did not consider several key players because of injury, including fly-halves Elton Flatley and Stephen Larkham, and key lock forward Dan Vickerman.
Seven members of the Australian Under-21 team, including hooker Tatafu Polota-Nau, flanker Leroy Houston, fly-half Scott Daruda and outside backs Digby Ioane and Cameron Shepherd are in the training squad.
In addition to the Under-21 representatives, prop Greg Holmes and scrum half Brett Sheehan have also been included, as well as openside flanker David Croft.
Jones said the size of the party was necessary because of fitness doubts over a number of players named.
"We've selected a squad of 45 because there are still a number of players we want to have a look at medically and physically, before finalising a group for the spring tour," Jones said.