The Black Cats have been heavily linked with Wolves striker Steven Fletcher as well as Blackburn Rovers pair Steven N'Zonzi and Martin Olsson and although O'Neill preferred not to comment on exactly who he is targeting, he did make it clear that he intends to bring some quality to the Stadium of Light.
"I can't obviously mention particular players, but we're definitely in the market to try to improve the squad," he told the Sunderland Echo.
"It's pretty obvious where we're looking to try to strengthen and of course we're going to be linked with a lot of players.
"It's not right to publicise what we're doing at this minute.
"But we have made a number of bids for a number of players and we're still waiting to hear back."