AC Milan must prove their strength without Zlatan Ibrahimovic against Inter Milan, coach Stefano Pioli said on Friday, after the Swede was ruled out of the Milan derby through injury.

The 40-year-old striker damaged his Achilles tendon during a draw with Juventus before the international break, and has not recovered in time to feature against champion Inter Milan.

Ibrahimovic is Milan's top scorer in Serie A with eight goals in 15 games, but Pioli challenged his players to perform in the striker's absence, as they did by beating Atalanta and drawing with Juventus on the road earlier this season.

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"It is a very important match, but we have had a lot of others like the last one in Bergamo and in Turin against Juve, but I'm sorry that Zlatan is out," Pioli told a news conference.

"We have grown a lot with Zlatan and now we must show that we are strong without him too.

"We need to have that willpower and spirit that has marked us out, especially in the delicate moments of the season."

Pioli said that Ante Rebic also won't feature through injury, while defender Fikayo Tomori is unlikely to start.

Saturday's clash at San Siro could be a pivotal moment in Milan's bid for the Serie A title, as it is currently third, four points behind leader Inter, which has a game in hand.

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"It carries a big weight, it means a lot for many reasons. It's the derby, winning it would bring confidence and be great for the league table," Pioli said.

"Inter are very strong, they are showing that again this year.

"The way the two teams play will create a lot of one-on-one battles, and the team that wins most of them will have more chances to win the game."