Winger Obertan has been sidelined with a slight hamstring tear.But the 24-year-old is expected to return to training next week to give manager Alan Pardew an extra option at Villa Park.
Williamson, meanwhile, also missed Newcastle’s first four games with a minor injury.
Alan Pardew: “I think Gabby will come back to us, and Willo will be fit.
“As long as we don’t pick up any knocks in training, we should have a good squad going to Villa.
“We’re in a lot better health with the result (last week’s win over Fulham).”
Obertan was linked with a loan move to Championship club Nottingham Forest last month, and Williamson was expected to sign for Cardiff City, but neither deal came off.
Steven Taylor, who has served a three-match suspension for his dismissal at Manchester City, will be in contention for places in central defence next week, but Mapou Yanga-Mbiwa has helped the Magpies to clean sheets in the last two Premier League games in his absence.