Tuesday's sports briefs

Serena Williams grabbed her racquet and got out on a tennis court Tuesday, which she said was her "first day back" after a series of health problems, including blood clots in her lung.

The 13-time Grand Slam singles champion has not played an official match since she won the title at Wimbledon in July.

On Tuesday, Williams tweeted: "Cool news guys stay tuned.. Ill update u with a pic.. U ready??"

Then, a little while later, she tweeted again: "Look who I spotted on the court. Her first day back..." That posting came with a link to a photo of Williams in a neon pink body suit, standing at the baseline and midway through her service motion with a racket in her right hand.

Her agent, Jill Smoller, confirmed the 29-year-old Williams put in some work Tuesday.

Shortly after claiming her fourth singles championship at the All England Club last year, Williams cut her foot on glass at a restaurant, an injury that led to two operations. The second surgery was in October, and she said she spent 10 weeks in a cast and 10 weeks in a walking boot.

The 29-year-old American then was diagnosed in February with blood clots in her lung. After that, she said she needed treatment for a hematoma -- a gathering of blood under the skin -- on her stomach.

Lionel Messi scored his club-record 48th goal of the season as Barcelona advanced to the Champions League semifinals with a clinical 1-0 victory at Shakhtar Donetsk, easily protecting its 5-1 advantage from the first leg against its Ukranian opponent. Barca likely will face Spanish archrival Real Madrid in the semis.

In England, host Manchester United got goals from Javier Hernandez and Park Ji-sung in a 2-1 victory over Chelsea, advancing 3-1 on aggragate goals. The Red Devils are in the Champions League semis for the fourth time in five years.

Beckham might return to MLS another year

David Beckham said there's a chance he will return to Major League Soccer after this season. His five-year contract with the Los Angeles Galaxy expires after this season, but the 35-year-old midfielder said he might play another year in the league, and wants to be involved with the England team at the 2012 London Olympics.

College basketball: Kemba Walker said Connecticut's decision to put his name and number on the wall of its basketball arena helped him decide it was time to head to the NBA. "It was like coach [Jim Calhoun] just kicked me out," the All-America said upon confirming his decision to leave UConn after his remarkable junior season. "It says 2008 to 2011 [on the banner], so it was like he's [saying], 'Let's get him out of here.' " ... Butler's Shelvin Mack wants to find out where he stands in the NBA draft. The 6-3 junior guard said he is declaring to enter the draft but has not hired an agent. ... Florida's Billy Donovan turned to a pair of fired head coaches to revamp his staff, hiring former Arkansas coach John Pelphrey and former St. John's coach Norm Roberts as assistants. Donovan also said assistant Richard Pitino is leaving to become the head coach-in-waiting at Louisville, where his father, Rick, is coach. ... Tommy Amaker turned down overtures from Miami (Fla.) and will remain the coach at Harvard.

Cycling: Italian Olympic Committee President Giovanni Petrucci said doping has become so rampant that his country's cycling federation needs to tell teams and riders "to stop because nobody believes you anymore." The ultimatum came a day after CONI said it would open an inquiry into about 30 high-profile cyclists, team officials and physicians allegedly involved in an extensive doping operation based in Mantova.