The Northern Irishman himself admits there have been "too many" poor performances as they have let slip a commanding seven-point lead over city rivals Rangers.

Philippe Clement's side have the chance to leapfrog the reigning champions at the top of the Scottish Premiership when they visit St Johnstone on Sunday, but what has gone wrong at Celtic Park?

'We have to be more aggressive'

Rodgers has previously voiced his disappointment at Celtic's recent dealings in the transfer market, but he concentrated his current squad's inadequacies in explaining a home draw for which "I take responsibility for".

"The performance level was nowhere near what we'd want," he told BBC Scotland. "It looked like we'd get away with it, win 1-0 and get a good result but a poor performance. But it was neither. So very disappointing.

"It's the nature of how we conceded - it's not the first time. We've been in the situation a number of times now where we've been in front and not taken opportunities to extend the lead and then we've given ourselves anxiety and given the opposition to something to hang on to."

Rodgers was at one with the supporters who voiced their disappointment from the stands.

Reaction to Kilmarnock's late goal on BBC Radio Scotland's Sportsound

"It's not a one-off - it's happened too many times," he said. "When you look at how the team's being doing from an analysis perspective, the defensive side has been the one area where there's been a drop."

Rodgers points to the continued absence of key centre-half Cameron Carter-Vickers, while right-back Alistair Johnston has been added to the injury list.

"That aside, we have to be harder to beat at times," he said. "We have to be more aggressive. To see out a game, you have to be able to do that. It's just happened too many times.

"We invited pressure, especially in the second half, [we were] not progressing the ball quickly enough through the team."

Rodgers now thinks the title race is "going to be tight".

"There's still a long way to go and I'm sure it'll be to and fro between now and the very last game," he said. "I said it was never going to be a procession. I've had to fight throughout my career and this is another great challenge."

Celtic lost aura of invincibility

Former Scotland midfielder Michael Stewart believes that, from a position where Celtic should have the league won by now considering their city rivals had to ditch manager Michael Beale, "we're in a position now where Rangers are the favourites".

"Celtic in the end looked like the away side," he said of the draw with Kilmarnock. "They looked dead on their feet. They were hanging on. Credit to Kilmarnock because they got the sense of that as well."

Stewart suggested that the advantage Celtic have in the quality of their squad and intimidation provided by the size of their support "very quickly starts to crumble when the opposition get a sense of things are not going well and I think that's where Celtic are now".

The former Heart of Midlothian and Hibernian midfielder thought the January transfer window was a "missed opportunity" for Celtic to bolster the squad with real quality.

"It takes a long time to build that invincibility," he told BBC Radio Scotland's Sportsound. "It can disappear very quickly and that's what's happened here. Brendan Rodgers will be scratching his head wondering what else he can do.

"The thing that struck me with Celtic under Brendan Rodgers the first time round was the intensity. They never let up, but if you watch them now, they don't have intense players."

Fellow pundit English believes there have been "bad mistakes" at boardroom level, with "recruitment virtually non-existent, but Brendan Rodgers does not get a pass".

"Celtic fans have an expectation," he said. "They are used to having great fun mocking Rangers, but there's no laughing matter for them now and they don't like it.

'Could see this coming - they are insipid, slow and predictable' - Celtic fan Chris Burley

"Brendan Rodgers, even though he hasn't had the players in he wanted, he still has enough firepower in this squad to get better results and performances out of this team and he's not doing it.

"He should not be immune from criticism. It's not all on the board. Maybe a lot of it is, but Brendan Rodgers is not doing his stuff."

English thinks the malaise is also at boardroom level.

"Celtic have picked some fights with the media over very little this season - similar to what Rangers did under previous administrations and it could be argued it's illustrative of a club that's lost its focus," he said.

"Poor summer transfer window, poor January transfer window, Rodgers asking for quality players publicly and not getting them, Rodgers coming over as a pale shadow of the vibrant manager of his previous spell, team looking vulnerable and big players going backwards in terms of form. And a better Rangers."

While some Celtic fans might be calling for a change of manager, the BBC pundits disagree.

"It would cost a lot of money and would send the distress flares over Glasgow," English added. "They have got to stick with him and hope he finds something more from these guys."