From Comcast SportsNetBOSTON (AP) -- Boston Celtics star point guard Rajon Rondo will miss the rest of the season with a torn anterior cruciate ligament in his right knee.The news came during Boston's 100-98 double-overtime win over the Miami Heat on Sunday in which Ray Allen returned to his old home court for the first time."New guys are going to get an opportunity now," Boston forward Paul Pierce said. "These guys haven't had a chance to really showcase what they can do."For the past five seasons, Pierce, Allen and Kevin Garnett made up the Big Three. After Allen signed with the Heat as a free agent in the offseason, Rondo joined that group -- and became the team leader with his ability to run the offense.He was chosen as the starting point guard for the Eastern Conference in the All-Star game in Houston on Feb. 17.Now the Celtics hope he can be ready for the start of next season."How far is that?" coach Doc Rivers said, "I don't even know how long that is. Eight months? Nine months? So he'll probably be ready, but I don't know.Rondo injured his right knee in Friday night's 123-112 double-overtime loss in Atlanta, a game in which the Celtics blew a 27-point lead, but Rivers said he didn't know when.He reported to the TD Garden on Sunday for a pregame shootaround but was taken to a hospital after complaining of pain.The initial report was a hyperextended knee, but tests showed the ACL tear.Rivers said he learned about 25 minutes before the game that Rondo wouldn't play. Word of the injury's severity came during the game."He was telling me he thought he pulled his hamstring," Rivers said, "Rondo will be fine. He just will not be fine this year."The team made the announcement during Sunday's win in the nationally televised game that snapped a losing streak that had reached six games despite back-to-back triple-doubles by Rondo."We've just got to rally around each other," Pierce said. "I feel for him. He was having such a good season. It's disappointing news."As Celtics players walked off the court through a tunnel toward their locker room, Rondo, dressed in street clothes, greeted them."I know he's sad. I'm sad for him," starting guard Avery Bradley said. "Whatever Doc wants me to play, that's what I'm going to do."Rondo was averaging career highs of 13.7 points and 5.6 rebounds along with 11.1 assists this season.Still, the Celtics are struggling to remain around .500, finishing the day with a 21-23 record, 2 12 games ahead of the Philadelphia 76ers for the eighth and final spot in the Eastern Conference.The Celtics have no true point guard behind Rondo. Rivers said he didn't know if they would try to add one.Jason Terry, known for his outside shooting, Courtney Lee, Leandro Barbosa and Bradley are the other guards. Each played at least 25 minutes Sunday with Lee starting in Rondo's place."We knew something was up at the beginning, but we didn't know how serious it was," Lee said. "Nobody can fill his shoes. That's what makes him great. So the only thing we can do is work as hard as possible and keep the momentum going from this game and have no letup."Rondo suffered a dislocated left elbow in the playoffs on May 7, 2011, when he became entangled with Miami's Dwyane Wade.Boston won 97-81, but Miami won the next two games to clinch the second-round series in five games.