It was expected Hamilton would be summonsed as a witness to give evidence in Munich's district court on the first day of the trial next Monday.
Former Force India driver Sutil faces charges of aggravated assault following an incident in a nightclub in Shanghai after last year's Chinese Grand Prix, a race Hamilton won on April 17.
Sutil is alleged to have struck Lotus team executive Eric Lux with a champagne glass, causing a wound that required 24 stitches.
Hamilton's lawyer, however, has now informed the court his client is unavailable due to a prior engagement with McLaren.
It is unclear whether the trial will now proceed without Hamilton or if a new date will be scheduled to ensure he can attend.