City scored 102 goals and conceded 37 on their way to the title last season but with four games remaining this term Pellegrini's second-placed side have notched 70 goals -- the highest in the league -- and conceded 36.
Captain Vincent Kompany has struggled for fitness and form this season, while French international defender Eliaquim Mangala has failed to live up to expectations following his move from Porto for a reported fee of 32 million pounds in August.
City's defensive frailties have allowed Chelsea to build a 13-lead at the top and Jose Mourinho's side could win the title on Sunday if they beat Crystal Palace at Stamford Bridge.
"It's difficult to say a lack of goals when we're the most scoring team in the Premier League," Pellegrini told a news conference.
"Compared to last season we scored less but it's not easy to score more than 100 goals in the Premier League. You can't do that every year, you always try but can't do it always.
"We'll see what we need, it's important to be balanced. We need to improve on goals conceded for next season, not just scoring goals."
City, who are second and level on 67 points with third-placed Arsenal, having played a game more, face Tottenham Hotspur at White Hart Lane on Sunday and will be without injured defender Kompany and Ivorian midfielder Yaya Toure.
City beat Tottenham 4-1 in October and Pellegrini is hoping for more of the same against a sixth-placed Spurs side fighting for a Europa League spot.
"Tottenham have good players and a good manager," the Chilean said. "They play always in an offensive way. They need also to qualify for the Europa League.
"We must try and be as near to the top of the table. We are two teams that play well and attack. I hope we play a very good game for the fans."
($1 = 0.6575 pounds)
(Reporting By Michael Hann; editing by Toby Davis)
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