Manager Martin O'Neill warned Celtic could be in "serious trouble" if they do not strengthen their squad despite resuming his supervision of the team with a 4-0 victory over Dundee United.
A dominant display seemingly banished concerns there might be lasting damage from Wilfried Nancy’s brief but torrid tenure, which saw Celtic lose six out of eight games.
O’Neill returned to oversee a first clean sheet since his final game in caretaker charge and equal the two biggest wins of the William Hill Premiership season, which also came under his watch.
Two first-half goals in five minutes from Yang Hyun-jun and Arne Engels sent Celtic on their way, with substitute Benjamin Nygren and Daizen Maeda netting after the break.
"I thought we played really well," said the 73-year-old. "It was nice to see players performing well, playing with confidence, and it was just nice to win."
O’Neill claimed it was "too early to assess" how well the players had reverted back to their 4-3-3 shape and added: "It does give you a boost. But Wednesday night (at Falkirk) is a big test for us."
O’Neill pointed out the importance of a goal-saving block from Liam Scales on Owen Stirton and also admitted his concern that Julian Araujo might have received a red card for a late tackle on Will Ferry.
"If the confidence is kind of fragile, then that sort of thing can change again, then it gives the opposition a big boost," he said. "But we rode that one out and we saw it through."
Celtic are yet to make a January signing after failing to meet their objectives in the previous two transfer windows.
O’Neill fears the squad cannot take many more injuries to key players with the likes of Jota, Alistair Johnston, Cameron Carter-Vickers and Kelechi Iheanacho missing.
"I am hopeful we are going to get some people in," he said. "But just when you think that something might happen, things change around.
"We obviously need to do it, even just to give help to the boys. Because this week was the only free week we have had since I’ve come to the football club.
"And from here on to I don’t know how long, we’re going midweek each time. So there’ll be no respite. If we pick up injuries to really key players here, we could be in serious trouble.
"We need some people in. And we are honestly working on it. It doesn’t seem as if you believe me, but we’re actually working on it."
