Shaun Maloney deputised for the absent Martin O'Neill in Celtic's Scottish Premiership clash with Kilmarnock as the 74-year-old continues to recover from a hospital procedure.
But O'Neill visited the players at their team hotel ahead of the Rugby Park encounter and is improving after his health issue.
Celtic announced earlier this week that the former Republic of Ireland manager had undergone a "small procedure" in hospital on Wednesday before being discharged the following day.
Assistant manager Maloney told Sky Sports ahead of the game: "He is doing better again. He came to the team hotel and spoke to the players but he just needs an extra few days. But he's good. He is definitely improving."
Maloney admitted the players would miss their manager's influence in the dressing room.
"It's been pretty similar [this week]," he said. "Where he comes into his own is match day, so we will definitely miss him but we will try our best to make it as good a level for the guys as it is under Martin."
O'Neill signed a one-year contract as Celtic manager in June with the option of a further season after leading the Hoops to the double in the second of two interim spells in charge last season.
He was in the Celtic Park dugout on Monday as they opened their league campaign with a 1-0 win over Dundee.
