The case came about after he testified at the trial of Mr Demjanjuk, who is accused of assisting with the massacre 27,900 Jews at Sobibor in 1943.
Mr Demjanjuk went on trial for war crimes in Munich in November 2009, but complaints of health problems have caused proceedings to be delayed.
A judge has now ordered him to appear in court despite this.
The Munich state prosecutor has launched an investigation into the Alex N case and will now decide whether to bring charges.
If they do, he will be the third alleged SS guard to face prosecution in the past year.