The Love Story star's eldest son was sentenced to 16 months behind bars in February (12) following a car crash last August (11), when he was arrested for driving under the influence of drugs.
But O'Neal, who last month (Apr12) announced he had been diagnosed with prostate cancer, reveals he's still yet to visit Griffin, 47 - the actor's son with late actress Joanna Moore.
During an appearance on U.S. talk show The View on Tuesday (01May12), he confessed, "I don't even know what prison he's in. They don't tell me."
He did not elaborate on who was banning him from finding out where his son is being held.
But O'Neal admits he has patched up his differences with his daughter Tatum - Griffin's older sister - and she has been taking care of her sick father after overcoming her own issues at a drug rehabilitation centre earlier this year (Feb12).
He added, "Tatum is out and about and doing much better, looks wonderful and is happy. She's always happiest when I'm ill because she can mother me and fawn over me and take care of me."
O'Neal has another son, Redmond, with the late Farrah Fawcett. He is also tackling substance abuse issues in a court-ordered drug treatment programme.