STEFFI Grafs father, Peter, is to undergo a lie-detector test about his private life, Bild newspaper claimed yesterday, to determine whether he is mentally ill.

Peter Graf has been detained since last August on fraud charges following his handling of Steffi's tax affairs.

"Papa Graf must now tell the truth about his friends, his marriage, his behaviour towards his daughter and also his sex life," the paper said.

The test will be carried out by a court-approved psychologist, Dr Georg Sieber of Munich.

Bild said the aim to was to find out whether the 57-year-old suffers from "pathological mental instability, problems with his conscience, stupidity or any other serious psychological anomaly."