The Premier League leaders suffered their first defeat of the season on Wednesday night (6 December), losing 2-1 in Ukraine in the Champions League.
With City already guaranteed top spot in Group F and a trip to Old Trafford on Sunday (10 December), Guardiola made seven changes for the trip to Ukraine, resting the likes of Kyle Walker and Raheem Sterling, while Vincent Kompany missed the game through injury.
For the first time this season City were made to look rather ordinary, going two goals down after strikes from Bernard and Ismaily before Sergio Aguero, who was introduced in the second half, scored a late penalty to halve the deficit.
While the result brought City's unbeaten record to an end after 227 days, Guardiola was adamant the defeat could prove a positive for his side.
"Its hurts, it is never nice to lose a game," he told reporters, according to The Guardian.
"I was [however] feeling we needed to lose – for the players, for the club. In the media people say things when you win and you can forget how to focus.
"We came here when our job was done in the Champions League. Now we are going to see how we react on Sunday. But I saw how we reacted after we went 2-0 down here and we passed it well.
"The world will not finish on Sunday no matter happens and now we will prepare for that game."
However, City could be without their captain on Sunday after Kompany was not included in the matchday squad on Wednesday. The 31-year-old made the 2,000 mile trip to Kharkiv with the rest of his teammates after being rested in the 2-1 victory over West Ham United and was expected to start at the heart of defence against the Ukrainian outfit.
Guardiola, however, admitted the Belgian was forced to miss the game with a fitness issue.
"Kompany didn't feel good," he was quoted as saying by the Manchester Evening News. "I wanted to make him play, but he didn't feel good so it was an opportunity for the others to play."
Kompany's omission will spark fears over his availability for the game against United this weekend, when the two-time Premier League winners' unbeaten league record could be severely tested.
City won at Old Trafford last season as Mourinho and Guardiola first met in the Premier League in what remains the last defeat United have suffered on home turf under the Portuguese coach. Since September last year, United have gone 40 games unbeaten at Old Trafford, setting a new club record in the process.
However, City have won four of the last six league meetings on their neighbours' turf and have lost only three times in the Premier League against their local rivals in the last six seasons.