Although it has not been confirmed, authorities believe the victims are Darrin and Kimberly Campbell and their two children, who rented the million dollar home in Avila, an upscale community near Tampa.
Col. Donna Luscynski, the spokesperson for the Hillsborough County Sheriff's Office, suggested that at least two of the victims may not have been killed by the fire.
"On two of the victims, there is upper body trauma. We have confirmed that there were fireworks scattered throughout the house and the fire was deliberately set with an unknown accelerant," she said.
The fire was reported before 6 a.m. Wednesday after a neighbor heard an explosion.
Colin Campbell, the couple's son, was a high school baseball star. His coach, Brian Grifone, said he hoped to become a professional player.
The other victim is believed to be Megan Campbell, the couple's teenage daughter.
Blake hasn't lived in the mansion for at least two years. He retired from professional tennis after the U.S. Open in 2013.
Celebrity Families of 2014 [PHOTOS]