Thomas had surgery on his troublesome ankle in May but joined in main training with teammates on Thursday.
Thomas told Nova 100 he expects to be available to play in two weeks time.
"I reckon a couple of weeks so when the boys are up in Sydney (round 20)," Thomas said.
"I think that's next weekend maybe. I'll hopefully have a run around (either) next weekend or the weekend after, (but) it probably won't be in the seniors."
Thomas told AFL Media at the start of July he was refusing to give away his season, despite such a serious injury.
"All going to plan, hopefully, by the latter stages of the year, I'll be thereabouts," Thomas said at the time.
He has progressed his training load over the past few weeks and now needs to build up the required match fitness to ensure his return is fruitful.
Thomas is out of contract at the end of this season, but outgoing Magpies football manager Geoff Walsh insists the star Pie's signature is imminent.
"I don't expect there's going to be any issue there," Walsh told Sportsday last month.
"I don't think this is going to be drawn out because I know Dale wants to re-contract with the club, and certainly the club wants to re-contract 'Thommo'."
Collingwood faces a crunch game against Essendon on Sunday afternoon at the MCG, with Magpies skipper Nick Maxwell expecting the Bombers to come out all guns blazing in support of embattled coach James Hird.
