Next month, Salim Ahmed Hamdan, a Yemeni who was once a driver for Osama bin Laden, could become the first detainee to be tried for war crimes in Guantánamo Bay, Cuba. By now, he should be busily working on his defense.

But his lawyers say he cannot. They say Mr. Hamdan has essentially been driven crazy by solitary confinement in an 8-foot-by-12-foot cell where he spends at least 22 hours a day, goes to the bathroom and eats all his meals. His defense team says he is suicidal, hears voices, has flashbacks, talks to himself and says the restrictions of Guantánamo “boil his mind.”

“He will shout at us,” said his military defense lawyer, Lt. Cmdr. Brian L. Mizer. “He will bang his fists on the table.”

His lawyers have asked a military judge to stop his case until Mr. Hamdan is placed in less restrictive conditions at Guantánamo, saying he cannot get a fair trial if he cannot focus on defending himself. The judge is to hear arguments as soon as Monday on whether he has the power to consider the claim.