The Sun says O'Neill desperately needs to strengthen his squad after losing Olof Mellberg, Thomas Sorensen, Scott Carson and Patrik Berger in the summer.
But O'Neill said: "Although the players did fantastically last season we had the smallest squad in the Premier League, and we wouldn't want that to be the case this season, so we are going to address it.
"If Gareth Barry had decided to stay we were still going to address it. Now it's even more important than ever we do it. It's all systems go."
O'Neill also hit back at Barry's criticism he had been more interested in Euro punditry than Villa.
He said: "It was a case of working there for two or three days then coming back and working here."