And Mancini promised plenty more from Sergio Aguero after the Argentinian's sensational debut against the Swans.
The club's ?38million record signing came off the bench to score twice and set up another as City opened their Premier League campaign with a 4-0 hammering of promoted Swansea.
Aguero was an unused substitute for last week's Community Shield defeat and was kept waiting again at the Etihad Stadium until Edin Dzeko had broken the deadlock just before the hour.
Within moments he had turned in a Micah Richards cross at the far post and volleyed across goal for David Silva to tap home.
Yet the best came in injury time as the former Atletico Madrid playmaker fired a vicious shot into the top corner from 30 yards.
Mancini said: "I know Aguero very well but I don't think he is 100%.
"He has worked for only one week with the team.
"He needs to improve but he is a fantastic striker
"He played in the Copa America and he needs to do more in training, but I am happy because he scored two important goals."
Mancini was pleased to get a campaign in which his side are expected to challenge for the title off to a winning start.
He added: "It was the perfect start. It was important to start the season very well and it was important to score the goals and score with the strikers.
"But the season will be very long and very hard, every game is very difficult.
"In the first half Swansea played very well."
Mancini left controversial striker Mario Balotelli on the bench while wantaway Carlos Tevez was not in the squad.
Despite that, Mancini insisted all his forwards would still have a role to play.
He added: "We have four important strikers and they can play together."
Swansea made a composed start but were ultimately outplayed by the hosts, who also hit the bar twice through Silva and Gareth Barry.
But manager Brendan Rodgers is convinced the Championship play-off winners will make an impact in the top flight this term.
Rodgers said: "I thought overall the result - although there were some fantastic goals - was harsh on our team.
"For the first hour the players showed great confidence and great quality on the ball and we looked like we could be a real threat.
"Obviously the two quick goals around the hour-mark gave them more confidence and they started to express themselves a bit more, like the world-class players they are.
"You come off the pitch having been beaten 4-0 but I said to my players, 'Congratulations, you have put on a terrific show tonight'.
"We will get better and we want to improve.
"We understand now - like we did before the game - that if you make mistakes at this level you get punished.
"I was very proud of the club, it was a historic night.
"We showed we can be a threat in this league and we will take all the positives from this game and go again on Saturday."
Source: Team Talk
Source: Team Talk