CAIRO — A Cairo court sentenced an atheist from a Christian family on Wednesday to three years in prison for insulting religion, firing up fears about the future of freedom of expression here just as Egyptians prepare to vote on an Islamist-backed draft constitution denounced by secular groups as failing to protect such rights.

The convicted man, Albert Saber, is expected to be released on bail of about $167 pending an appeal. An open and avowed atheist, Mr. Saber, 27, was initially accused of circulating links to an offensive online video lampooning the Prophet Muhammad that set off protests across the Muslim world in September. Mr. Saber has denied promoting the video, and he is being charged for other statements critical of Islam and Christianity that police investigators found on his computer. Open profession of atheism is almost unheard-of in Egypt and is widely considered an affront to society as a whole.

Although blasphemy was a criminal offense under former President Hosni Mubarak before Egypt’s revolution as well, Mr. Saber’s case has raised special alarm because it comes against the backdrop of the sometimes violent battle over Egypt’s draft constitution, which elevates the crime of insulting religion to the level of the charter itself.

“Expect to see many more blasphemy prosecutions in the future now that it’s embedded as a crime in the constitution,” said Heba Morayef, a researcher with Human Rights Watch who is tracking the case.