Shaquille O'Neal (R) of the Miami Heat, and LeBron James, of the Cleveland Cavaliers, dancing together during NBA All-Star basketball practice in Las Vegas in this Feb. 17, 2007 file photo. O'Neal says on Twitter, Wednesday, June 1, 2011, that he's 'about to retire.' [Agencies]

BOSTON - Shaquille O'Neal, who struggled to get on the court for the Boston Celtics because of leg injuries, said on Twitter on Wednesday that he is going to retire after a 19-year career in which he won four NBA titles and the 2000 league Most Valuable Player award.

O'Neal sent a tweet shortly before 2:45 pm saying, "im retiring." It included a link to a 16-second video in which he says, "We did it; 19 years, baby. Thank you very much. That's why I'm telling you first: I'm about to retire. Love you. Talk to you soon."

An inveterate prankster who gave himself a new nickname - or several - in each of his six NBA cities, the 15-time All-Star did not notify his latest team of his plans. He played just 37 games this year, the first of a two-year deal at the veteran's minimum salary, making just three brief appearances after February 1.

"To my knowledge, he has not informed any of us that he's retiring," Celtics spokesman Jeff Twiss said.

If he goes, O'Neal retires fifth all-time with 28,596 points, 12th with 13,099 rebounds and second only to Artis Gilmore among players with more than 2,000 baskets with a .582 field goal percentage.

O'Neal's contributions to basketball went far beyond his presence on the court.

One of the most charismatic players in NBA history, O'Neal was a franchise-saver when the Orlando Magic made him the No. 1 overall pick in the 1992 draft. He took them from the lottery to the playoffs in two years, and then led them to the NBA finals in his third year before they were swept by the Houston Rockets.

O'Neal, 39, signed with the Los Angeles Lakers in 1996 and had his greatest success there, winning three titles alongside Kobe Bryant and coach Phil Jackson. But amid tension between O'Neal and Bryant over credit for the team's success, O'Neal was traded to the Miami Heat in the summer of 2004, fresh off a loss to the Detroit Pistons in the finals.

After 3 years in Miami, a tenure that included his fourth NBA championship, O'Neal became a veteran-for-hire, moving to Phoenix and then Cleveland and finally Boston. But he couldn't deliver another title for Steve Nash and Amare Stoudemire with the Suns, with LeBron James with the Cavaliers or with the Celtics' Big Three of Kevin Garnett, Paul Pierce and Ray Allen.

At each stop, he endeared himself to the fans and his new teammates with his effervescent smile and playful attitude, including the habit of adopting a new nickname that he felt embodied his role with his new team. In Phoenix he was the "Big Shaqtus"; in Boston, the "Big Shamroq."

He also embraced social networking, amassing almost 4 million followers on his Twitter account, where fans could find out his next move or even the "random acts of Shaqness" - like sitting in Harvard Square, pretending to be a statue, or going out in drag on Halloween.

But O'Neal's off-court persona couldn't disguise the fact that he was getting old, and while he showed he could still play with younger opponents he couldn't manage to stay on the court with them. He missed a week in November with a bruised right knee, a week in December with a calf injury and another in January with a sore right hip.

He returned for three games - a total of about 34 minutes - before missing the next 27 games with what the team called a sore right leg. Although the injury was originally expected to keep him out just a few games, his absence stretched to more than two months.

He returned to play in one more regular-season game but lasted just 5 minutes, 29 seconds before reinjuring the leg and limping off the court. He missed Boston's entire first-round series against the New York Knicks and made two appearances against Miami, a total of 12 minutes, and scored two points.

In all, O'Neal averaged just 9.2 points, 4.8 rebounds and 20.3 minutes this season while playing in 37 games - all career lows.