Milan slumped to a surprising 5-2 home defeat to struggling Sassuolo on Sunday which saw them drop to fifth on the Serie A table.
It marked the second straight game Pioli's side have shipped four or more goals, having also lost 4-0 to Lazio in midweek.
Pioli's side also lost 3-0 to Inter Milan recently in the Italian Super Cup.
AC Milan are now 15 points behind leaders Napoli and Pioli accepts it is time to re-evaluate their targets for the season.
"I'm thinking about many things," he told Sky Sport.
"Everything that has worked over the past two years isn't working right now.
"It's clear that if you want to change results, you have to change something. I'll make the decisions that are needed to bring us more compactness, energy and better balance."
"To say I'm disappointed doesn't cut it," Pioli added.
"These recent performances have left us in difficulty, but this must push me to understand certain situations must be improved.
"We have to react. We probably won't be able to win the Scudetto again. Instead, our Scudetto is fighting to finish in the Champions League spots, which we can achieve."
Pioli led Milan to their first Serie A title in 11 years last season.
