The German crashed in the stadium section with some four minutes of the session left when he drove over the white line in the tricky conditions. His car suffered heavy damaged on all four corners and practice was red-flagged.
The seven-time champion said the accident was his fault.
"Basically I've not been fully concentrated. I was on the radio and I was doing some other changes to the car and touched the white line," said Schumacher of his crash.
Schumacher finished in 23rd position on a very tricky day for the teams, with rain coming and going both in the morning and the afternoon.
The German conceded the changeable conditions meant the day was not too useful.
"It didn't help us a lot, because the conditions were so inconsistent that we couldn't learn a big deal," he said.
He said, however, that it was worth running in the wet as qualifying is also expected to be hit by rain on Saturday.
"It is what it is, so you have to make the best of it. We are going to qualify probably in wet conditions so that's why it makes sense to go out and try the car and get the set-up right and so on. But it's guesswork for Sunday, definitely."