Australian tennis coach Nick Philippoussis has suffered a massive stroke in a US jail and will likely never face trial on charges he sexually assaulted two young girls he trained in California.

A San Diego judge was told on Thursday 68-year-old Philippoussis, the father of former world top 10 Australian player Mark Philippoussis, is catatonic after the stroke and has been held under guard and handcuffed to a bed in a public hospital for several months.

The criminal case is now on hold pending Philippoussis' health.

"He is conscious, but is not responding to any stimuli," Philippoussis Sr's lawyer Ryan Tegnelia said.