Pioli has succeeded Marco Giampaolo at the San Siro and will be looking to turn around the fortunes of a club who have lost four of their opening seven Serie A games.
Milan welcome a Lecce side all of whose six points this season have come away from home and Pioli, who will celebrate his 54th birthday on the day of the game, wants total commitment from his new team.
"My players won't have to worry about being perfect – tomorrow it will be impossible to seem totally organised – but I expect a lot of desire and focus," he said at a press conference.
"I have quality players, tomorrow I will better understand the technical and physical characteristics of each one.
"So far the players are giving me everything, everyone is fine and everyone expects to play, the attitude is right and it will always have to be."
Milan have lost their last two home games, but Pioli is still aware of the size of the club and feels ready for the challenge ahead.
He lasted just six months as Inter boss before being sacked in May 2017, before two seasons in charge of Fiorentina.
"I'm at a prestigious club with a great history, it's an honour and a proud moment to be here," he said.
"If you coach Milan, playing at the San Siro doesn't have to be a worry, but an extra motivation.
"I feel like I am ready to coach at this level. Over the years I have learned above all from the bad experiences that have improved me both from a technical and a human perspective.
"I feel I have matured."
Struggling Lecce go into the game on the back of two straight defeats, but boss Fabio Liverani will not send his team out purely to frustrate their hosts.
"I do not believe that only by defending we will be able to score points," he said on the club website.