The Italian's concern is likely to raise a few eyebrows among those who have watched the world's richest club spend hundreds of millions of pounds putting together an outfit to mount a serious assault on the Premier League title.
The league leaders have been depleted this month by the departures of Yaya and Kolo Toure, who are on Africa Cup of Nations duty, while captain Vincent Kompany has been handed a four-match ban after a red card against Manchester United on Sunday.
With Carlos Tevez frozen out and fellow strikers Edin Dzeko and Mario Balotelli struggling with knocks, City are a little short-staffed even if the players they do have available are worth more than many clubs can dream of.
"All the people think we have a lot of players," Mancini told a news conference ahead of Wednesday's League Cup semi-final first leg against Liverpool. "But we have 19 plus keepers. It is not a big squad.
"If we are unlucky and we have three or four players injured, like at this moment, we can have a problem. The club knows this."
Mancini last week suggested City could dabble in the transfer market in the January window providing they sold some players first, such as Argentina striker Tevez and former England defender Wayne Bridge.
Since being taken over by Sheikh Mansour in 2008, City have spent more than 600 million pounds on players.
They disclosed an annual loss of 194.9 million pounds in their financial results for 2010/11, the biggest ever in English soccer.
Conscious of the need to comply with UEFA's financial fair play rules which come into full effect in 2013/14 and which aim to stop reckless spending on wages and transfers, City have spoken of moving towards more sustainable spending levels.
Splashing the cash has yielded rewards with the club winning their first major trophy in 35 years with victory in last season's FA Cup final.
They competed in the Champions League for the first time this term, going out at the group stage, and have established a three-point lead at the top of the Premier League to give themselves a good chance of dethroning rivals Manchester United.
Player absences, though, have come at a time Mancini has earmarked as key to their chances of picking up some more silverware.
"I said four weeks ago that December and January would be crucial months," said Mancini.
"Until three weeks ago we didn't have any injuries. Now we have a problem.
"We have players injured and others who went to the African Nations Cup at a crucial moment. I am not happy about this but we can't do anything about it."
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