Celtic made three loan signings on transfer deadline day, securing striker Junior Adamu from Freiburg, winger Joel Mvuka from Lorient and defender Benjamin Arther from Brentford.
The Scottish Premiership champions also rejected an approach from Nottingham Forest for midfielder Arne Engels.
Czech Republic forward Tomas Cvancara arrived from Borussia Monchengladbach earlier this month, as did Bournemouth’s Mexico defender Julian Araujo, with those deals also loans.
O’Neill, who is in charge until the end of the season, was quick to close down the idea the club were only interested in temporary arrangements.
“The January window is difficult for permanent deals,” he said, suggesting that winger Fares Ghedjemis chose to stay with Frosinone in Serie B, while others had gone elsewhere for “probably pretty big money”.
O’Neill added: “The players we were going to spend money on, I believe, would have helped us,” before saying that his missed targets would have been “difficult not to like” for his successor.
