"Depends on the day I talk to him. Paul has had the summer, he's gone back and forth," Rivers said while back in Boston to host the annual ABCD Hoops Dream fundraiser at TD Garden. "I think he has a right to do that. I really do.
"Paul didn't have the best year last year. I don't think he wants to go out that way. So I think that's why he's working to try to come back. But he still may change his mind next week. So we just have to wait. I told him if I see him at training camp, I'm assuming he's playing."
Rivers plans to talk with Pierce again this week but does not expect an answer until training camp draws closer.
Rivers said he would be brutally honest with Pierce if he didn't think Pierce was capable of helping the Clippers next season.
"If I don't think they can play, then I tell them that. But I think Paul can play," Rivers said. "I don't know how much he'll play, but he can play. I've always thought it's easy for someone else to tell you to retire; I think that's something that the player has to come to by himself."
Rivers reaffirmed that, should Pierce choose to retire, he'll encourage him to sign a one-day contract with the Boston Celtics in order to retire as a member of the Celtics organization.
"I think it's important. I think we have to do that. And I think we will," Rivers said. "[Celtics president of basketball operations] Danny [Ainge] and [assistant general manager] Mike [Zarren], we've already talked.
"The day [Pierce] retires, he's going to retire a Celtic. He has to. Paul's a Celtic. So when he retires, he's got to retire as a Celtic. I don't think anyone disagrees with me."
During an 11-minute chat with reporters, Rivers was peppered with questions about his former Celtics Big Three of Pierce, Kevin Garnett and Ray Allen -- with all the questions centering on whether Rivers thought any of them would play during the 2016-17 season.
Rivers could only laugh when it was noted that he thought each of those players had a limited playing window when the Big Three came together for its title run in 2007.
"I told the guys when we got them together, 'We've got to win this year. I don't know how long you're playing,'" Rivers said. "I thought like two or three years. So I was a little wrong on that one, for sure."
Rivers talked with Allen this summer but wouldn't tip his hand on whether he thought Allen would resume his NBA career after sitting out the past two seasons.
"I don't know. I won't talk about what we talked about. I think if Ray was in the right spot, he may play," said Rivers. "I think Ray wants to golf a lot too, right now. But Ray is in amazing shape. I don't know how he does that. I didn't know how he does that as a player; I don't know how he does it as a non-player. He's probably in top-5 shape in the NBA. So could Ray play? Absolutely, I believe he could."
Rivers sounded most confident that Garnett would continue his playing career, even as he aids the rebuilding process with the Minnesota Timberwolves.
"I think Kevin -- and I know it, because I talk to him -- loves the young guys on his team," Rivers said. "He loves how they work. He thinks they have an old-school mentality. So I think he's really gotten into Kevin, the teacher. And I honestly never saw that coming, either. Yet he was a phenomenal teacher with [Boston]; I just didn't think he would have the patience to do it. And I think Kevin loves teaching these young guys.
"And I think Paul just loves playing. He was the one that I thought would play the longest because the way he plays, and he's doing it."