Celtic cannot “live off the the past”, warned manager Neil Lennon, after they were outplayed in defeat by Rangers.
The champions – without six players because of Covid-19 and injury – succumbed 2-0 to trail Rangers by four points with a game in hand.
Celtic have won the last 11 domestic trophies and are bidding for a record 10th consecutive Scottish title.
“We have a title race on our hands and we have to roll our sleeves up and do better,” said Lennon.
“They have done it before but we can’t live off the past either, this is the present.
“It’s been disruptive with Covid and a lot of players away on international duty and I’m not sure some were on the ball today mentally. It looked like what we were – a team put together before the game.”
Lennon gave AC Milan loanee Diego Laxalt a debut at left-back, while 20-year-old defender Stephen Welsh made his second appearance, and Polish striker Patryk Klimala was handed a rare start.
But Celtic ended without a shot on target as a Connor Goldson goal in each half deservedly earned Rangers back-to-back derby wins for the first time in 11 years.
“I thought we deserved to go in at least level at half-time, we missed a great chance to equalise with Mohamed Elyounoussi,” said Lennon.
“But we gave away two really poor goals and Rangers defended their box better than we did. We have players who are not fully fit coming on and they didn’t have the impact we hoped.”
Lennon revealed that Odsonne Edouard, who had to self-isolate after testing positive for Covid-19 with France Under-21s, is also likely to miss Thursday’s Europa League group opener against AC Milan.
“We can’t take a chance on anyone’s health and he wasn’t ready anyway,” the Celtic boss added.
“I doubt he’ll be okay for Thursday. It’ll be the same for [Nir] Bitton and Hatem [Elhamed] but Ryan [Christie] will hopefully get the all clear this week.”
Celtic’s Old Firm line-up was leaked online on Friday night and Lennon vowed to investigate the “disgusting” breach, adding: “Somebody within the club is doing us in.”