The Brazilian suffered the ignominy of being substituted after coming off the bench for Roque Santa Cruz, who sustained a calf problem, in Saturday evening's 2-0 defeat by Everton at Goodison Park. Mancini explained his reasons for bringing on Shaun Wright-Phillips after seeing his side suffer their first defeat in five games in all competitions since he replaced Mark Hughes last month.
"I had (Craig) Bellamy, Benjani (Mwaruwari), (Carlos) Tevez, Robinho - all strikers - so I decided to take one off," said Mancini.
"I needed a different kind of player.
"Is it the end of the line for Robinho? No. He is a good player. Like everyone in the squad he needs to work hard and play well."
Goals from Steven Pienaar and Louis Saha (penalty) gave Everton a deserved victory and damaged City's hopes of clinching a Champions League place.
Mancini admits they need time to develop and knows things will not happen overnight.
He may dip into the transfer market but stressed: "I am not a magician. I am a manager and I do not think I can change the situation in a month.
"But I believe we can improve game after game. That is possible. It is a long season."