O'Neill says he will cast a wide net as he looks to strengthen his Black Cats squad and admits the free agent market - and the speed with which those players might need to be recruited - has been very much in his thoughts.
"We will be looking in every market," said O'Neill, quoted in the Sunderland Echo.
"But I agree that there might be one or two players available on Bosmans who are really worthwhile and can be an asset to the football club.
"We will have to be sharp and quick off the blocks though, because anyone who is half-decent will not be available for long. It has more than crossed my mind, already."
O'Neill, who succeeded Steve Bruce as Sunderland manager in December and led the team to a 13th-placed finish in the Premier League, is particularly keen to bolster his striking options.
"It has been a very busy six months, but it has at least given me the chance to look at the squad and decide where we need to bring in reinforcements," O'Neill said.
"Obviously, when you look at the fact that no-one reached double figures in terms of goals for us last season, that is one area we need to address.
"But there are other areas I would like to look at too."
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