Kubica accepted blame for the crash, which occurred on the final stage of the day. He had lost the lead to Jan Kopecky - who kept it for the rest of the day - in the morning after a puncture in the wet weather.
"We slid into the bank, and just as I thought we'd get back on the road we were suddenly on our side, and then we rolled," Kubica, who stands ninth after losing four minutes in the crash, said.
"We managed to finish the stage, despite an issue with the front suspension. We tried to fix it after the stage, so we could drive back to service, and now we will see how bad the damage is.
"I was just surprised by how the car reacted in that corner.
"I wasn't pushing, to be honest, I was driving at normal speed I would say, but unfortunately there was very poor grip at that corner, and we lost the car as the result of a mistake.
"I nearly managed to get the car back but the bank got bigger, which put us on our side and we rolled.
"The rollcage seems OK. It was a difficult day, ending with this mistake. As for tomorrow, we will see if we manage to get the car sorted out."
His mechanics at PH Sport managed to repair the Citroën DS3 RRC, which suffered extensive damage.
Kubica’s engineer Kevin Struyf said: “We changed the front left and the rear left suspension because it was broken when Robert hit the bank.
"We changed the driveshaft in the front left. After that we made some work on the body shell and the rear spoiler. But there was no problem with the engine, we checked everything.”
The DS3 was also fitted with a replacement windscreen, two rear side windows and rear spoiler.
Kopecky did not set the pace on any of the three afternoon stages but takes a 13.1-second lead into Saturday, which will feature seven stages.
Irishman Craig Breen (Sainteloc Peugeot) is second with a 20s advantage over Bruno Magalhaes (Delta Peugeot).