Sunday's 1-1 draw at home to Cesena leaves Inter nine points off the UEFA Champions League places with 11 games to go. Mancini's side needed Rodrigo Palacio's goal just after the break to rescue a point at San Siro.
"With a win we would've climbed to 39 points with 11 rounds to go," Mancini told Sky Sport Italia. "Now it's going to be pretty difficult to reach third place.
"With a victory we could've had hope, but there are too many teams in front of us now.
"At the moment there's no point talking about third place and it's not even logical to do so.
"I think all players want to do better, but unfortunately this team is improving slowly and alternating good performances with negative ones. We can only work and it might take more time to improve.
"Perhaps it is my fault, I am an optimist by nature and thought we could achieve something more in less time. It's bad for our fans, as they suffer, but we are suffering too."
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