Kensington Palace on Monday said Meghan Markle was suffering a "deeply personal moment" following reports her father would not attend her wedding to Prince Harry on the weekend.
According to celebrity news website TMZ, Thomas Markle, who recently posed for paparazzi photos, has pulled out of accompanying his daughter down the aisle at Windsor Castle because he does not want to embarrass her.
Mr Markle is also reported to have suffered a heart attack in recent days.
"This is a deeply personal moment for Ms Markle in the days before her wedding," Kensington Palace, the official residence of the couple, said in a statement.
"She and Prince Harry ask again for understanding and respect to be extended to Mr Markle in this difficult situation."
The palace refused to confirm whether her father would be attending the wedding on Saturday.
The US actress' father had previously defied the palace's pleas for secrecy by agreeing to pose for a paparazzi photoshoot.
The images, showing him being measured for a suit and admiring a photo of the future royal couple on his computer, sold for $100,000 (83,000 euros, £74,000) according to tabloid the Daily Mirror.
A source close to Thomas Markle, cited by the publication, said he was convinced after being hounded by the paparazzi. He is now said to feel "like a total fool" who has been "scammed".