The Northern Irish boss says that he is waiting to hear back from two bids he made recently for players.
"We have made bids for a couple of players, but we didn't make them overnight, we made them some time ago," said O'Neill. "Of course, it's absolutely the prerogative of the team to whom we have put these bids in either to accept or not accept as the case may be.
"We wouldn't be the only club in that sort of position, this idea that we are waiting until January 31.
"There may be a host of signings in the next 48 hours, I don't know, but there's every possibility because that seems to have been the way of it in the last number of years."
Sunderland travel to face Reading on Saturday.