Mancini had said on Sunday that the 21-year-old had played his last game for the club this season following his red card in the defeat at Arsenal.
Balotelli, who picked up a three-match ban for the dismissal, received no further punishment by the Football Association for his tackle on Alex Song in the same match.
Mancini has now insisted that he only made his original comments because he thought that the forward would be given an additional ban retrospectively.
"I thought Mario would be banned for six or seven games, that's why I said he wouldn't play again this season," said the Italian.
"He only got three games so I'm pleased for this. He will be back for Manchester United, he will be ready."
City, who are now five points behind United in the table, host their local rivals at the Etihad Stadium on Monday, April 30.