But Pierce expressed gratitude for what Allen brought to Boston, including helping the Celtics win a world title.
"Ray made the best decision for him," Pierce told the team's official website Thursday in his first public offseason comments. "That's what it's all about: You get in these situations, you become a free agent and you make a decision based on what's best for you and your family. Ray will always be a brother for me. If it wasn't for him, I probably wouldn't be wearing a championship ring. So the things he was able to do for this organization will never be forgotten."
Asked if he has talked to Allen since he spurned Boston's two-year, $12 million offer to sign with Miami for half the value, Pierce said, "A couple texts. I'm a little bitter that he went to Miami, but he's still a brother of mine."
Pierce said that despite the departure of Allen, he is a fan of what Celtics president of basketball operations Danny Ainge and his staff have been able to do this offseason reassembling much of the core, highlighted by a three-year contract extension for Kevin Garnett.
"I love what Danny's been able to do," Pierce said. "It was a tough decision this summer. A lot was riding on what direction we were going to head in. It was just a domino effect, once we signed Kevin, we knew were going to try to make another run at it. That's pretty much the way I looked at it. Once we signed him, a number of guys were able to jump on board.
"I thought Danny did a good job of trying to replace Ray Allen. As you know Ray Allen went off to Miami, on his choice, but he was a great teammate, it was fun playing with him. But I think the guys coming in here -- Jason Terry, Courtney Lee, trying to get a healthy Jeff Green, even some of our rookies -- I think we've added a lot more depth, and it's going to take a lot of pressure off me this upcoming season."
As for who he's most excited to play with next season, Piece pointed to Terry.
"I've always been a big fan of Jason Terry," Pierce said. "Playing against him in college for a couple years, then watching his NBA career flourish over the years. From winning a championship to just bringing that element to our ball club now -- he's one of best sixth men all-time to play the game. That's something we were lacking a year ago, and that was only due to injuries, so hopefully he can bring that consistency, that championship experience, so we can get back to where we were a few years ago."
As for his health, Pierce admitted a sprained MCL, suffered during a walkthrough in the first round of the postseason, hindered him the remainder of the playoffs, but he didn't want to use it as an excuse for his diminished play. Pierce said he has spent much of the offseason strengthening the area around the knee while it heals.
"The knee is a lot better. It's not completely healed, but I figure I'm about 90 percent now," Pierce said. "So I've been doing a lot to strengthen it, so I can come back a stronger player. It really hampered me, I thought, the last 10-15 games of the year. I couldn't explode like I wanted to. But everybody was hurt at that point of the year. Everybody was dealing with nagging injuries. That's why I didn't really stress on it too much in the playoffs, because I know everyone is dealing with injuries and that's just another excuse."
Pierce said he focused on strengthening his quad and hamstring to alleviate stress on the knee. He said that workout included a lot of stair work and light running on the treadmill. But he noted, "It's been responding very well."
Pierce expressed "fresh excitement" for the new season and noted, "We're going to build on what we did last year. I think we're more talented. We were able to bring back Brandon Bass -- we brought back our starters and then added to it. I think we have a deeper and better bench. Hopefully, it reflects better in the playoffs, so that we can go for a championship."