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Ibrahimovic was suspended last weekend as Milan won at the San Siro for the first time in over two months against Genoa.
But the 39-year-old Swede and French left-back Theo Hernandez have both been hampered with muscular problems.
Midfielders Hakan Calhanoglu and Ismael Bennacer are also struggling with knocks.
"We have problems for Bennacer, Ibra, Calhanoglu and Theo, they all had difficulties training. Let's see tomorrow (Wednesday)," Pioli told a pre-match press conference.
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Ibrahimovic is Milan's top-scorer with 15 goals in 17 league appearances this campaign.
Veteran Croatian forward Mario Mandzukic returned after a long injury layoff against Genoa.
"Mandzukic did well and made his presence felt," said Pioli.
"He can't play for 90 minutes, but I count on him. He will help us."
Second-placed Milan are nine points behind city rivals Inter with seven games left, including against top-four rivals Lazio next Monday, and Juventus on May 9.
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