Kilmarnock 1-0 Celtic: Brendan Rodgers says his side paid for blunt attack
Celtic manager Brendan Rodgers said his side paid the price for failing to create chances against Kilmarnock.
The Rugby Park side delivered only the second domestic defeat of Rodgers' spell in charge, with Youssouf Mulumbu scoring in the 1-0 win.
Rodgers felt his side wasn't assertive enough, but also hampered by injuries to Dedryck Boyata and Kristoffer Ajer.
"We could've played here until midnight and not scored. We weren't really threatening," Rodgers said.
"We were disappointing. Defensively, we were a bit passive at times, even though we didn't have so much defending to do.
"We can blame injuries, we can look at the pitch and all sorts where it's very difficult to play, but the bottom line is we weren't so good today. Very disappointing result."
Rodgers will not know the full extent of Boyata's groin problem and Ajer's ankle injury until the two players undergo scans on Sunday, but he is already without goalkeeper Craig Gordon and striker Leigh Griffiths for the Europa League last-32 tie against Zenit St Petersburg on 15 and 22 February, while German defender Marvin Compper could also miss out.
The Celtic manager felt the lost of the two defenders - Boyata in the 10th minute, Ajer in the 35th minute - affected his team's display.
"It doesn't help, certainly, when you lose two of your back three so early in the game," Rodgers said.
"It means you've got to change and alter people's positioning and obviously differ your plans. With the ball, with so much talent on the field, we didn't create a great deal either."
Kilmarnock manager Steve Clarke said his players were rewarded for the discipline of their play but also bringing the commitment and organisation of their work on the training ground into competitive games.
The win was Kilmarnock's fifth in a row at home, and moved them into the top six before the rest of the Premiership games had kicked off.
"We kept our shape, we believed in what we were trying to do and when we grew into the game we started to play some really good stuff," Clarke said.
"When you look at the game overall, there's not too many people that would grudge us that win.
"It's easy to do it on the training pitch. The hardest thing is to take that level of quality into a big game like that, against the best side in the country by a distance.
"I've got belief in these players. If we can continue that in the coming weeks then we can have a decent season."
Kilmarnock striker Kris Boyd said the team worked during the week on closing down space in the middle, to deny Celtic room in the final third.
"Celtic didn't really cut us open, we were organised and we worked all week on being compact in the middle of the pitch," Boyd said.
"In the first half we had numerous opportunities to put the ball into the box and didn't do it, but in the second half we did and you saw the difference. We could have had two or three others after that.
"We said it from day one when the manager came in, there was a change because he brought that experience, he's been at the top level. From the first time that he spoke to us we knew that if we listened there was going to be a change in the fortunes of this club. We've put a run of games in now at home."