Milan, also out of the Champions League, already look to be out of the title race after losing four matches this season.
While Italian media reported that defeat on Saturday could lead to his sacking, Pioli disagreed.
"We need a win. I expect a convincing performance," Pioli told a press conference.
"Tomorrow's game isn't about me, nor is it do or die, there's still a long way to go in the season. Milan must win tomorrow because we need the points. We cannot expect to make up for everything tomorrow."
Milan won the Serie A title with a 3-0 win at Sassuolo in 2022, but Pioli is also aware that his team have lost the last three meetings between the sides at the San Siro.
"We've studied Sassuolo, they are a side that builds from the back and creates chances. We need to be aware of (Domenico) Berardi and (Armand) Lauriente, in particular," Pioli said.
"But they also concede a lot too, so we'll have to take advantage of their frailties, especially in defence. Sassuolo have beaten Inter and Juventus, which means they know how to play certain games, and possess quality."
Milan have struggled with injuries this season, which may go some way to explaining why they have been unable to put together a winning run to keep pace with the league leaders.
"Our flaw is that we haven't had consistency. The new signings are strong players, but then it's normal that it takes time to adapt to the Italian league," the manager said.
"It's not the best league, but it's certainly the most complicated in terms of tactics and pressure."
Milan are third in the standings, on 33 points after 17 games, seven behind Juventus in second and just two ahead of Bologna in fourth. Sassuolo are 15th with 16 points.
