Milan angry with official
The Rossoneri were held to a 1-1 draw by Lecce and vice-president Adriano Galliani was unhappy with some of Pieri's actions.
Galliani felt Milan skipper Paolo Maldini was harshly treated in receiving a yellow card and felt the official should have dismissed Lecce's Cesare Bovo for a bad foul.
"It has been a technically inadequate refereeing display," said Galliani.
Maldini's caution will hit Milan particularly hard as it rules him out of the derby with Internazionale at the weekend.
The veteran defender was upset with the performance of the referee, as he said: "Unfortunately the referee had double standards.
"As for the foul on Tomasson, I spoke with him and he told me that Bovo was looking for the ball.
"In the episode involving me, I didn't see the Lecce player and he didn't see me. It was not an intentional foul."
Coach Carlo Ancelotti was equally unhappy, saying: "Maldini's yellow card isn't right.
"We should have played for 30 minutes with a numerical superiority because Bovo made a really bad foul on Tomasson and he had already received a yellow card.
"I repeat the referee can make mistakes on offsides, on corners and on free-kicks, but over these episodes, and I'm referring to Maldini's and Bovo's ones, he can't be wrong."