Mr. Giambi had a six-year major-league career spanning 510 games, including 82 with the Philadelphia Phillies
The reason of death was unknown at the time. According to agent Joel Wolfe, Mr. Giambi died at his parents' house in Southern California.
Former Phillies pitcher Brett Myers tweeted Wednesday night, "RIP Jeremy Giambi!" "I'm saddened and horrified to learn about my old teammate's loss!
Mr. Giambi was a sixth-round draught selection of the Royals in 1996 as a five-sport athlete (baseball, basketball, football, golf, and bowling) from South Hills High School in West Covina, Calif.
Two years later, he made his major-league debut for Kansas City. He was traded to the A's before the 2000 season and spent two years with his brother, reaching the postseason both times.