Mancini enjoyed a turbulent relationship with the controversial striker, who ended his stay in Manchester by moving to AC Milan in a €23 million move on deadline day.
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"It was difficult," Mancini told reporters. "It was only my decision. Until one week ago it was impossible [to sell him] because we didn't receive any offers.
"Instead in the last three days Milan started to talk with the club and made the offer.
"We thought it was good for everyone. For Mario, it could be a big chance to go back to Italy and play for a top club like Milan and we hope it will be important for him. For the club, we can get back some money."
Mancini also denied reports that he was happy to see the back of Balotelli after many public fall-outs with the striker, and has backed him to do well back in Milan.
"We are not happy," he added. "Mario did well, maybe not in the last three or four months because he had big problems with injury, but he did well because he helped the team win the Premier League and the FA Cup.
"We are sad [to see him go] but this is football.
“He has everything, always. He has quality. It is important he can understand this."