Nick Philippoussis appears frail as he pleads not guilty to molesting two nine-year-old girls

Nick Philippoussis looked frail when he appeared in handcuffs in a San Diego court, charged with sexually abusing two nine-year-old girls.

The 68-year-old appeared in the Superior Court in Vista, north of San Diego, around 7am (AEST) and pleaded not guilty to 14 counts of child molestation charges.

The charges related to two alleged victims, both girls aged nine, between 2016 and 2017, the court heard.

He faces a maximum jail sentence of 210 years to life if convicted.

Nikolaos Philippoussis is the father of former Australian top 10 player Mark Philippoussis. He has been in custody since sheriffs raided his home in San Diego on Tuesday.

Philippoussis Snr's lawyer Ryan Tegnelia however said his client was innocent and would fight the charges.

Philippoussis' family, including Mark, were in shock after the arrest but were supporting him.

"This caught everyone completely flat footed," Mr Tagnelia said.

The judge raised his bail to $US9.2 million ($AUD12 million). His lawyers did not oppose it, saying he would be unable to raise the money anyway.

Mr Tagnelia said Mark Philippoussis has offered to provide any comfort for his father during his jail stay.

Because of the child sexual abuse charges, Philippoussis Snr is being kept in protective custody.

Mark Philippouss, who attended the court hearing, did not answers reporter questions as he left.

Yesterday, he also dodged questions 9NEWS regarding the arrest.