MIAMI — Alonzo Mourning has decided to retire rather than mount another NBA comeback at age 38.

The seven-time All-Star center said today he won't return from a devastating leg injury in 2007. He's not under contract but had been working out at the Miami Heat's complex and still had a spot in the team's locker room.

Mourning hasn't played since tearing the patella tendon and quadriceps muscle in his right leg on Dec. 19, 2007, the fourth anniversary of his lifesaving kidney transplant. He said he feared another return would put his health in jeopardy.

"I truly feel it's best that I retire," Mourning said at a news conference. "When you've got something you love and you're passionate about, it's hard to let that go. But at 38 I feel I've physically done all I can for this game. It has been an amazing ride."

Mourning, who turns 39 next month, played at Georgetown and was the second overall pick in the 1992 draft by the Charlotte Hornets. He also played for New Jersey but spent the majority of his career with the Heat, helping them reach the playoffs six consecutive years. He was the backup center to Shaquille O'Neal when Miami won the NBA title in 2006.

At age 30, Mourning was diagnosed in October 2000 with focal segmental glomerulosclerosis, a career-threatening kidney disease. He missed most of the ensuing season but rejoined the Heat in March 2001 and made the All-Star team the following year.

When his condition worsened, he missed the entire 2002-03 season and underwent a transplant in 2003. Again he returned, but for three consecutive summers beginning in 2005, Mourning considered retirement before choosing to keep playing.

"It's not a sad day, but it's a day to celebrate," Mourning said. "I can think of a million people right now that would have loved to walk the path I've walked. The ups and the downs made it even more joyous."

In 15 seasons, Mourning averaged 17.1 points and 8.5 rebounds and twice was chosen NBA defensive player of the year. He averaged 6.0 points and 3.7 rebounds in 25 games last season for the Heat.

Mourning has long supported charitable causes in Miami and campaigned for better education. He attended President Barack Obama's inauguration on Tuesday.