Ronny Deila insists his vision for Celtic has not been changed by Saturday's 2-1 home defeat to Motherwell.
It looked like the Ladbrokes Premiership leaders would get away with a largely lifeless display when midfielder Nir Bitton's deflected shot four minutes after the break put them ahead.
However, a double from Well striker Louis Moult, the second from the spot after Hoops stopper Jozo Simunovic tripped former Celt Scott McDonald, gave the visitors their first win at Celtic Park since 2008.
It was Celtic's first home domestic defeat since they lost 1-0 to St Johnstone in March - but they have also now gone four matches at Parkhead without a win and were booed off by their fans.
The result left Deila's side one point ahead of chasing Aberdeen with a game in hand over the Dons and they now prepare for the trip to Hearts next Sunday.
Asked if the performance showed that his side needs strengthening in January, the Norwegian replied: "You have to see the bigger picture, the whole season so far.
"We know what we want to do and that picture is no different now than before the game.
"Domestically we have been good at home. I was (surprised). I didn't expect that performance otherwise I would have done something about it.
"It was very disappointing and there was a lot of stress in the end.
"In the last 30 minutes at 2-1 down we had to move the ball quicker and get the crosses in.
"We had our chances but when you play so open you will get punished, so that is something we have to do totally different next Sunday."
Deila refused to blame the defeat on the absence of top scorer Leigh Griffiths and skipper Scott Brown.
Griffiths, who signed a new contract on Friday that ties him to the club until 2021, missed his third consecutive game with a calf injury - although his boss expects him back for the trip Tynecastle - while Brown is out long term with a knee problem.
"That is easy to talk about but all the team that played has also played the games that we won earlier," said Deila. "I won't use that as an excuse.
"We've so many good players and they have shown earlier that we can beat teams domestically.
"It was a bad performance and that is something that we have to admit and turn around."
Mark McGhee was in his first spell as Motherwell manager when they beat Celtic in 2008 thanks to a Simon Lappin goal.
The former Celtic striker praised 23-year-old former Wrexham striker Moult, who took his tally for the season to 11, and strike partner McDonald for their efforts since he returned to the Lanarkshire club in October.
He said: "I'm a great fan of Louis. I think the two strikers, Scott McDonald and Louis, have done well since I've been here.
"I think Scott was terrific as well, but Louis scoring the winning goals at Parkhead is a great step in his career.
"He's a terrific player. He's aggressive, he's got a great touch and he's got a goal in him so he's an all-round striker."