Photos of Spears, her husband, Kevin Federline (search), and the couple's infant son were published online Friday, but were taken down within hours after her record label, Jive Records, issued a statement threatening legal action.
"When a person like her, who's obviously a sweet person, is having their first child, it's like, 'leave the girl alone,'" Timberlake told "Access Hollywood." "I do think that's crossing the line," the 24-year-old singer said. "That's her baby and those are her baby pictures."
The pictures, taken in a private photo shoot, were allegedly stolen. Spears reportedly has been negotiating to sell them to a magazine.
The Web site tangiblebrit.com, which was the first to post the photos, withdrew them. A message on the Web site says: "To Britney, Kevin, Sean, Jive Records, SonyBMG and anyone else I have affected by this, I am deeply sorry for any pain I have caused you."
Spears' baby, who was born Sept. 14, hasn't been seen in public, nor has his name been announced, though reports say it is Sean Preston Federline.
The baby is the first child for the 23-year-old pop star and Federline, 27, who has two children with ex-girlfriend Shar Jackson.
After his breakup with Spears in 2002, Timberlake was viewed as parodying her in the video for his hit "Cry Me a River" from his first solo album, "Justified."
Timberlake has dated Cameron Diaz since 2003.