Sizemore said the photos -- one of them showing him nearly nude -- were stolen from his girlfriend's e-mail account and posted online. He contacted baseball officials to stop the spread of the photos, which began appearing Sunday on various Web sites.
It is not known how many sites are complying with MLB's request. At least one site, deadspin.com, is refusing to take the photos down.
"There's no reason to," editor A.J. Daulerio said Monday. "They were up other places already."
Daulerio said the photos originated on a community message board and were forwarded to his site, which is also displaying a letter from an MLB official requesting the photos be removed.
The letter reads: "The photos posted in the article cited below are the property of Grady Sizemore. They were stolen from a personal computer. We've begun an investigation and request that you immediately remove Mr. Sizemore's property from the posting. We also ask that you preserve any records associated with its submission in anticipation of a criminal complaint to be filed with local law enforcement."
MLB investigators are trying to determine how many sites ran the photos of Sizemore standing in front of a bathroom mirror in various stages of undress. Sizemore used a cell phone to take the pictures of himself. He told The Plain Dealer of Cleveland they were intended only for his girlfriend.
The Indians said Sizemore wouldn't make any further comment on the photos.
"We fully support Grady as he deals with this personal matter," the Indians said in a statement Monday. "The posted photos were stolen from his girlfriend's e-mail account and a legal investigation is under way."
The 27-year-old Sizemore is the Indians' most popular player. His fan base includes "Grady's Ladies," and several other women's groups devoted to the three-time All-Star.
With a rare combination of speed and power, Sizemore has developed into one of baseball's best all-around players. He is one of only two players in club history to hit 30 homers and steal 30 bases in one season.
A two-time Gold Glove winner, Sizemore has endeared himself to Cleveland fans with his hustle and durability. In 2006 and 2007, he played in all 162 regular-season games, but he was limited to just 106 games last season.
Sizemore suffered an elbow injury and sports hernia during spring training in 2009 and was never 100 percent. He batted a career-low .248 with 18 homers and 64 RBIs before he deciding to stop playing on Sept. 4. He underwent two offseason surgeries.