"Starting again in Bologna after the Kaka affair gives us enthusiasm and a different charge," Ancelotti told the Serie A club's website after Kaka came off the bench to help them beat Hanover 3-2 in a friendly on Wednesday.
Last Saturday's 1-0 win over Fiorentina at the San Siro had the flavour of a goodbye, with players queuing up to embrace the Brazilian at the end of the match and fans showing banners and singing chants pleading the 26-year-old to stay.
Milan's travelling support will be in a very different mood this weekend, after the club said on Monday that the 2007 Ballon d'Or winner and FIFA world player of the year is staying.
Captain Paolo Maldini said that Kaka's loss would have hit the title hopes of third-placed Milan, who narrowed the gap on leaders Inter Milan to six points with victory over Fiorentina.
"We are all really happy," Maldini told the club's in-house TV channel. "It would have been a big blow to lose Ricardo (Kaka) after having recovered three points on Inter.
"There aren't any players comparable to Ricardo, who has given so much to this team and can really become a symbol of Milan."
Kaka helped Milan win the Serie A title in his first season after moving from Sao Paulo in 2003 and he was the driving force behind their seventh European Cup triumph in 2007.
Ancelotti will be without the suspended Marek Jankulovski for the trip to Bologna, who are hard to beat despite their low position in the standings (16th) and stunned Milan 2-1 at the San Siro on the opening day of the season.
Inter will be without suspended Sweden forward Zlatan Ibrahimovic on Sunday when they entertain Sampdoria.
Their advantage over second-placed Juventus has dropped from six points to three over the last two league games, a 1-1 draw with Cagliari and last week's dismal 3-1 defeat at Atalanta, when the champions were lucky not to lose by a bigger margin.
Coach Jose Mourinho hopes to have stopped the rot with Wednesday's 2-1 win in the Italian Cup over holders AS Roma, which booked his side a semi-final meeting with Samp.
"We showed that we are a team," he told Rai television. "The players responded very well to Sunday's negative performance and did their talking on the field."
Juventus host sixth-placed Fiorentina in Turin on Saturday.
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