Lotus driver Romain Grosjean admitted that he made "a stupid mistake" in Japan, where Mark Webber branded him "a first-lap nutcase", but said that it was time to move on.

Grosjean, slapped with a one-race ban over a first-corner crash in Belgium, was at it again at Suzuka on Sunday, driving into Webber seconds into the race and so robbing the Australian of the chance of a podium finish.

A furious Webber suggested the Frenchman might need another "holiday", or ban, and labelled Grosjean's driving "embarrassing". Grosjean's team also warned the 26-year-old to curb his overly aggressive style.

Grosjean said he was looking forward to making amends this weekend at the Korean Grand Prix.

"Since Singapore (on September 23, after his ban), I've been trying to be really cautious at the starts and it's been all the more frustrating to be involved in an incident in Japan," he said.

"When approaching the first corner, I was watching Sergio (Perez) on my left to make sure there was no contact with him. I didn't expect such a big speed difference between me and Mark (Webber) braking into the corner, we collided and that was it."

"It was a stupid mistake. Mark came to see me after the race and was obviously not happy, but I apologised and we have to move on," he told the official Formula One website.

"I've sat down and looked at things again with the team, for sure it's still an area we need to improve. We're clearly focusing on this area for the next races."

Grosjean was given a 10-second stop-and-go penalty in the pits in Japan and retired from the race towards the end when it became clear he was out of the points.

Red Bull's Webber had to scramble to rejoin the race and then made a pit stop for running repairs, returning at the back of the field before racing hard to finish ninth.