Roberto Mancini feels his Manchester City side must improve quickly if they are to qualify for the Champions League knockout rounds.
Mancini's side host German champions Borussia Dortmund in Group D on Wednesday, looking to bounce back from a losing start.
City lost their opening match 3-2 to Real Madrid on 18 September after conceding two late goals.
"If we want to go through, we need to improve very quickly," Mancini said.
City's task in qualifying from Group D is a tough one, having been drawn with the champions of Germany and Spain, as well as last season's Dutch Eredivisie winners Ajax.
"This is the second year for us in the Champions League and the second year that we got the worst group," Mancini said.
"Like we have improved [over the years] in the Premier League, we need time to improve in the Champions League, but we don't have a lot of time - only five more games, and we need to improve quickly.
"We need to not concede easy goals to drop points like we did against Real Madrid."
Mancini has declared that Joleon Lescott remains an important player for City, even though he has only started two of their last four matches.
City have yet to keep a clean sheet this season but defender Lescott, 30, was an unused substitute against Fulham last Saturday.
Lescott could again miss out against Dortmund, but Mancini said: "He is one of the best defenders."
City have conceded eight goals in six Premier League games this season having kept 17 clean sheets on their way to the title last season.
Lescott, who has 23 England caps, was also an unused substitute when City leaked two goals in the final three minutes to lose in Madrid.
"I have six or seven defenders and I made a different choice last week and in Madrid," added Mancini.
"On Wednesday I will decide again, but Joleon is an important player for us."