The Northern Irishman admitted that moves for new players have "stalled," and tipped young winger James McClean to improve once again this term
The Black Cats are reported to have made a £10 million bid for Wolves striker Stephen Fletcher, but the 60-year-old boss has revealed that he is not the only target they are currently working on bringing to Wearside.
However, he admitted that negotiations are not as advanced as he would like - but hopes to have signed some new faces by August 18.
"We have made some bids for players, and we are obviously in negotiations with the football clubs at this moment," O'Neill told reporters.
"It seems to have stalled somewhat on all fronts, but I am hoping to improve the team - I think we have to give ourselves some sort of chance for next season. I think that's pretty obvious.
"In an ideal world, I would like the players in so they could do some work before we play against Arsenal. If that's not the case, then we will work exceptionally hard to try to get the players in before the end of the month."
O'Neill also singled out 23-year-old winger James McClean for special praise - saying that he looked sharp in training, and did not expect his form to dip after a barnstorming breakthrough season.
"It is a big season for him. There is obviously always talk about second season syndrome, that type of stuff, but I don't think it will affect him," the former Celtic boss added.
"He has come back and done exceptionally well in training here. He looks every bit as strong as he was before, and he looks every bit as determined."