Hill, 34, who won last Sunday's San Marino Grand Prix on the same track to take the lead in the world drivers' championship for the first time, had spun off the circuit when he collided backwards with the wall.
A Williams official said: "Damon is all right, but the car is seriously damaged at the rear end. He spun off and hit the wall backwards. It was a big impact."
The car was not instantly judged to have been written off. "The boys have got a fair bit of work to do to repair the car overnight," said the official. "It is pretty bad."
Hill's crash was not the only problem for the championship- leading Williams team on a hot day at the Autodromo Enzo Dino Ferrari.
The team's other driver, the Briton David Coulthard, suffered a scare when his engine burst into flames while he was out on the circuit. The fire was controlled quickly and there was no serious damage to the car. Coulthard was also unhurt.
The Austrian, Gerhard Berger, led the day's practice times with a best lap of one minute and 28.88 seconds, three-tenths of a second better than Coulthard.Reuse content