AC Milan must transform the disappointment of its midweek defeat to Atletico Madrid into positive energy, coach Stefano Pioli said on Saturday ahead of his side’s Sunday night Serie A clash with Atalanta.

Milan surrendered the lead to lose 2-1 to the Spanish Champion in the Champions League on Tuesday, and felt hard done by after Franck Kessie was sent off in the first half before Luis Suarez converted a winning penalty deep in stoppage time.

"Defeats must give you positive energy. We never put games behind us, we always analyse them," Pioli told a news conference.

"We need to transform this defeat into positive energy, because tomorrow will be a clash with a direct rival."

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Atalanta was also in midweek European action, beating Switzerland’s Young Boys 1-0, and it can cut the gap to second-placed Milan to two points with a win in Bergamo on Sunday.

"Last year Atalanta were second until the final day of the season, we have a lot of respect for them but also conviction in our quality," Pioli said.

"Atalanta are strong in every way; tactically, technically, physically. They have players who can produce a decisive move at any moment, but we also have these characteristics. Tomorrow will be like a Champions League match."

Kessie's future has been a topic of much discussion in the Italian media recently, with the Ivorian in the final year of his contract.

But Pioli dismissed the notion that transfer speculation is impacting his performances.

"It does not worry me because Franck's attitude is the best possible, the same that he has always had in the past, in terms of work, seriousness and professionalism," Pioli said.

"It is wrong to judge his performances based on his contract. I consider what he shows on the pitch, there are a lot of players in a lot of teams with expiring contracts where there is not this much clamour.

"There is a negotiation ongoing, the time will come for a decision, negative or positive. I am not concerned."

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Milan striker Zlatan Ibrahimovic celebrates his 40th birthday on Sunday, but Pioli said the Swede will not be ready to return from injury until after the international break.

"I do not know how many years he can keep playing, but from what I see, his enthusiasm and desire for training, I would say he could play forever," Pioli said.