The Rossoneri had been on top of the Serie A table until their surprising 2-2 draw with Pisa at San Siro.
Christian Pulisic, Adrien Rabiot, Pervis Estupinan and Ardon Jashari are still out of action.
Leao is partnered by Gimenez rather than Christopher Nkunku, while Ruben Loftus-Cheek is back on the bench after shaking off a muscular problem.
Fikayo Tomori returns to the defence after being dropped in favour of Koni De Winter.
Atalanta are the only Serie A side to remain unbeaten so far this season, but that doesn’t translate to a successful run, because only two of those were victories and they’ve drawn four on the bounce.
With Nikola Krstovic and Gianluca Scamacca struggling for goals, coach Ivan Juric opts for De Ketelaere and Lookman together supported by Mario Pasalic.
These are familiar faces, as both De Ketelaere and Pasalic are former Milan players, so are Yunus Musah and Daniel Maldini on the bench.
Giorgio Scalvini and Mitchel Bakker are the only remaining absentees.
