A homeless man charged with brutally attacking an 82-year-old Sikh man outside a gurudwara in the US city of Fresno, in an apparent hate crime, will be sent to a psychiatric hospital until he is fit to stand trial.

Judge W Kent Levis made his decision on Monday in Fresno County Superior Court after doctors concluded that Gilbert Garcia Jr, 30, is unable to assist in his defence to charges of attempted murder and elder abuse.

The police said Garcia attacked Piara Singh, 82, with a steel rod outside of the Nanaksar Sikh Temple at Cherry and North avenues in south Fresno, California on May 5.

Singh's injuries included broken ribs and head wounds, the Fresno Bee reported. In the state hospital, Garcia will be required to take anti-psychotic medication.

He will remain at the hospital until he is competent to stand trial, but his stay can be no longer than 15 years, the judge said. Typically, inmates spend less than a year in a state hospital before their competency is restored, lawyers said.