Glasgow's Alex Dunbar has joined fellow centre Mark Bennett and Peter Horne as fitness doubts for the opener, with Richie Vernon out of the Championship.
Matt Scott was the only centre able to train fully on Monday with Duncan Taylor recovering from a dead leg.
"If you look at Peter Horne, Mark Bennett, Duncan Taylor, Matt Scott, there is depth there," said O'Halloran.
"So that's really comforting for me; we have four quality centres right there that we can choose from.
"I'm excited about the talent, there are a lot of guys playing well.
"Mark Bennett is an outstanding young talent, Duncan Taylor has been playing really well for Saracens and has a bit of knowledge about England with the defensive system Sarries run. So he is a valuable guy.
"Matt Scott is playing well, Stuart Hogg is starting to play some really good rugby. Finn Russell is a really good player at this level and is coming off an excellent World Cup. Greig Laidlaw is an outstanding leader of the group."
O'Halloran said Scotland's medical team are "pretty confident Mark [Bennett] should be alright for England" after a shoulder injury, with the possibility he could feature for Glasgow in their Pro 12 game against the Ospreys on Sunday.
But Horne's recovery is "on the backburner" after he suffered a recurrence of a foot problem.
Head coach Vern Cotter called up Glasgow prop Alex Allan and Edinburgh back-row Hamish Watson as cover for training this week.
Scotland took the Wooden Spoon in last season's Six Nations but were two minutes away from beating Australia in their World Cup quarter-final and are in a positive frame of mind.
"They are coming off a solid World Cup and will have learned a lot about playing in big games like this," said former Manawatu Turbos head coach O'Halloran.
"I certainly think we can carry a lot more confidence into games. If you are more familiar with your role and understand it better, you can really bring another level of physical intensity to the game, and that's really where our focus is."
Glasgow Warriors prop Zander Fagerson believes Scotland can win the Six Nations, but O'Halloran was more grounded with his ambitions.
"I don't know about winning it, we just have to take one game at a time and the first hurdle is England, which is going to be a massive, massive challenge with Eddie [Jones] in there as the new coach and a lot of disappointed players after the World Cup," explained the New Zealander.
"So they will be really hungry and wanting to make a statement and we have to match their physical intensity."
Backs coach Jason O'Halloran believes injuries will not weaken Scotland against England in the Six Nations.