Pellegrini accepts having chalked up 100 goals in all competitions so quickly, there was always going to be a spell where things did not run so smoothly in the final third.
"To score goals is always the most difficult thing in football. Maybe because this team has been scoring goals so easily this season, people have been talking about the amount of goals they are going to score again," he said.
"I think that this is absolutely related to the injury of Aguero. Negredo and (Edin) Dzeko are not 100 per cent fit to play as well as they did before, but we must continue.
"We are right behind the leaders, have 39 points more to fight for and this team were favourites to win the title with the way we were playing.
"We must try, as soon as possible, to play that way (again)."
Pellegrini added: "Although we drew here, it is not the last game that we are going to play.
"We have 13 games more to fight for the title.
"Every team will drop points. Last week, it was Chelsea against West Ham at home. This weekend it was Arsenal.
"We hope that we will continue fighting until the end."
City are still fighting on four fronts, with an FA Cup tie against Chelsea, the small matter of a Champions League showdown against Barcelona as well as the Capital One Cup final.
Pellegrini accepts even City's superb squad will be stretched over the coming weeks.
"It is not normal to have five players injured for an important game, and two or three more players were not 100 per cent," he said.
"I was concerned also about this match and next week we also have a very difficult week because we have three competitions to play in.
"We have a Premier League game to play in against Sunderland, then in the FA Cup against Chelsea then in the Champions League against Barcelona.
"We will see how we can recover the players during these days."
Pellegrini feels no definitive conclusions can yet be drawn in the championship race.
"It is very difficult to know who are the favourites," the City boss said.
"For me, the favourites were Arsenal because, after playing 25 games, Arsenal were leading the table for most of them.
"(Then) we were the favourites though, because we had been playing very well before this week.
"Chelsea are now playing well as well, but they are not the favourites - and don't forget about Liverpool, and maybe Everton or Tottenham.
"I think five teams are going to fight for the Premier League this season. This year the Premier League will be closer than ever."