O'Neill visited his side at their team hotel ahead of the Rugby Park encounter with assistant manager Shaun Maloney saying the Northern Irishman was improving after his health issue.
Celtic announced earlier this week that O'Neill had undergone a "small procedure" in hospital on Wednesday before being discharged the following day.
"He is doing better again," Maloney told Sky Sports ahead of the game: "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 added O'Neill's influence was missed 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."
No details were given about O'Neill's operation, which came after the veteran manager took charge of Celtic's win against Dundee in their first game of the Scottish Premiership season.
O'Neill signed a one-year contract in June to become Celtic's permanent boss for the second time after two interim spells last season.
He led Celtic to the Scottish Premiership title after a dramatic final-day win against rivals Hearts and also won the Scottish Cup.