Ancelotti is yet to commit his future to the champions elect beyond the summer with speculation he could move to Real Madrid should Jose Mourinho make his expected Bernabeu exit.
"I would be sad if he leaves. I've had a very good relationship with him in the 18 months that we've worked together," Pastore told a press conference.
"But those are the sorts of things that happen in football. You have to be ready for it."
PSG have been the dominant force in French football for the most part of this season, Ancelotti's first full term in charge, and can wrap up the Ligue 1 title at home to Valenciennes on Sunday night.
Ancelotti also guided PSG into the quarter-finals of the Champions League, where they were edged out by Barcelona on away goals.
"I would like him to stay, he's done great things for the club," Pastore said.
"But it's up to everyone to make their own decisions.
"We've had a very positive year in both the league and the Champions League. It was difficult at the start, but it's ended positively."