The 60-year-old has made just one signing this summer, with Aston Villa defender Carlos Cuellar moving to the Stadium of Light on a free transfer in July.
“I think that it may take an upturn in the not too distant future,” said O’Neill in the Northern Echo.
“Football clubs would have a look at last season and think where they can improve. There’s a group of us in that position.
“There may be something in waiting for the big clubs to make a move. I heard that Roberto Mancini is looking at five or six to strengthen.
“If Man City are in that position, God help the rest of us. There will be plenty of movement this month.”
O’Neill replaced Steve Bruce as Sunderland manager in December, and the Northern Irishman led the Black Cats from the relegation zone to a 13th-place finish.
Titus Bramble has been linked with an exit from the Stadium of Light after the Sunderland defender struggled to stay fit last season, but O’Neill revealed the former Newcastle centre-half still has a future at the club.
“Titus has had a few injury problems, but he’s over those now. A fit Titus Bramble is an asset to us, he needs to stay fit that’s the main thing.
“It’s an interesting one, we don’t want to overcook it but we need him properly fit. You might get away with half a game or one game, but if you’re in there you’ll get found out.
“We can’t have him going through seven or eight games.”
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