Thomas has been significantly hobbled by an ankle injury throughout the Magpies' pre-season, which stems from off-season ankle surgery.
The latest timeline puts in doubt Thomas' ability to be ready to face North Melbourne in round one on March 31.
"He'll need to get some solid training in and get up to speed before he starts playing any footy," Buckley said on Friday.
"Whether that's late in the NAB Cup or early in the home and away (season) will depend on the speed of his recovery.
"He's had a modified pre-season and got a lot of fitness work in, but obviously not on [his] legs.
"We'll have to judge that as we go, but clearly he's an important player for us."
Off the field, Thomas' contract talks are the source of major speculation, with fears they may resemble Travis Cloke's much publicised negotiations last season.
But Buckley would not be drawn on any discussion surrounding Thomas.
"We've got about 40 per cent of our list coming out of contract this year and we'll deal with those guys, appropriately, at the right times," he said.
One topic Buckley did touch on was the issue of player behaviour, which has gathered steam after Wednesday's drug summit.
"My charter is to prepare the team to win as many games as they can," Buckley said.
"A lot of that is about football, but an equal percentage is how they carry themselves as people, how they prepare and how they contribute to the environment for their teammates.
"We have strict values and expectations on how we expect our players to behave."
But Buckley said he would not be afraid to confront a player, if he thought they were not living up to the club's standards.
"The trick is to build a relationship with people and a trust within the environment of a football club that you believe you'll be able to have those hard conversations, about anything off or on the field," he said.
The Pies coach also said he was an advocate of clubs being informed of players who test positive after the second strike, under the AFL's three-strike drug policy.
"As a coach you would like to get as much information as you can to make the right decisions and push the buttons of your players at the right time," he said.
