Martin O'Neill acknowledged Celtic must "rethink" their approach and took full responsibility after more Old Firm disappointment on Sunday.

Celtic lost to rivals Rangers for the second time in the space of eight days, following up their 3-0 defeat in the Scottish League Cup at Ibrox with a 1-0 home defeat in the Scottish Premiership.

This defeat snapped a 13-game winning run for Celtic in the league, but problems do seem to be mounting for the Scottish giants.

Along with back-to-back defeats against Rangers, they were swept aside in the Europa League by Ferencvaros, but O'Neill does not see the need to rip everything apart.

"Nobody is pleased with what's happened, it's been a tough week. But history proves the football club fights back from these things," O'Neill told Sky Sports.

"When the players come back from international duty, we'll have a rethink. I don't think it's a disaster. And the word they tell me is 'reset'. It's time for a bit of self-reflection."

Ryan Naderi scored the only goal, pouncing on a rebound for the first-half winner as a largely flat Celtic performance was punished.

Indeed, Celtic had just five shots, managing only one on target, and created chances worth only 0.71 expected goals.

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— Celtic Football Club (@CelticFC) September 20, 2026

"Every defeat is really painful, and it hurts every bit as much now as it did before," O'Neill added to BBC's Sportsound.

"I have to reflect on things myself, see what I can do better to help the team. That's something that I'll genuinely think about.

"There are always big questions when you lose football matches. You have to accept responsibility, which I do. Remember, this is the team, this is my team. I am responsible for that introspection.

"We've got work to do. [Three successive defeats are] an unusual occurrence for me; it's an unusual occurrence for Celtic football club, and I am responsible for that."

It was an entirely different story for Derek McInnes, who became only the second Rangers manager to win both of his first two Old Firm derbies against Celtic, after Graeme Souness in 1986.

"Really pleased, we had to deliver a big performance and we did exactly that. It's not easy coming here, the circumstances you're under and what you face," he told Sky Sports.

"We knew we'd have to overcome a wounded Celtic team. We played with a lot of confidence. I'm disappointed we didn't add to the goal we did score, because we were deserving of that.

"At 1-0, you still think they'll get a chance and we're kicking ourselves a wee bit that we didn't take another chance. It was a worthy win, after what was a disappointing start in the league."