Leao was hooked at the break in a triple substitution with the Rossoneri trailing 2-0 along with Brahim Diaz and Pierre Kalulu, with Pioli bringing on Ante Rebic, Sergino Dest and Charles De Ketelaere.
The Portuguese forward has been subject of transfer interest from big clubs including Chelsea and Manchester City, yet he wasn’t spared.
Leao missed two early chances, before Koffi Djidji and Aleksey Miranchuk put Torino two goals ahead.
Pioli explained: “I wanted to change something, seek more movement off the ball, vivacity and the push of Sergino Dest rather than Pierre Kalulu. I looked for different characteristics in the strikers.
“It certainly wasn’t his best evening, that was fairly obvious. We started better in the second half, but then needed to get a goal back a bit earlier. Its a pity, as this is a defeat that hurts.
“I am certainly disappointed, because we expected a different performance and result here tonight.
“It must make us work even harder going into the next games, so we should react immediately and show a different side to the team.”
The result ends Milan’s 17-game unbeaten away run, while it is another crack in their title defence, sitting in third spot and six points behind leaders Napoli who won 4-0 over Sassuolo.