Thomas attempted to play on after a collision with Swans ruckman Mike Pyke during the first quarter of Saturday night's match, but was eventually substituted.
"It's just a corked thigh and is nothing too serious," Director of Football Geoff Walsh told the Magpies' website.
"The club's medical staff said today that he should be alright to play against North Melbourne."
Simon Buckley and Caolan Mooney will both make a push for selection, but will need to undergo tests to prove they've overcome hamstring injuries.
