The Frenchman faced intense criticism - and a face-to-face confrontation with his Australian rival – for the part he played in a crash with the Red Bull driver at the second corner at Suzuka.
Coming so soon after Grosjean's race ban for the Belgian Grand Prix startline pile-up, Webber and Red Bull chiefs suggested that the Lotus driver's behaviour was 'unacceptable.'
Grosjean has apologised to Webber for the incident – which came, he says, because he was trying so hard to avoid a crash with Sergio Perez that he misjudged his closing speed to the car ahead of him.
"Since Singapore, 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," explained Grosjean.
"When approaching the first corner, I was watching Sergio 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 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.
"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."
Team boss Eric Boullier reckons rivals are pushing Grosjean hard because they know he has to be cautious – and thinks the Frenchman's latest problem has come from trying too hard to not crash.
"We could see in Singapore, when Romain was back after his race ban, that some other drivers were putting extra pressure on him at the start," he explained.
"In Suzuka, Romain made a small mistake by misjudging his pace relative to Mark, which was a bit higher. We have sat down and spoken.
"We understand what has to be done. I think in Singapore to an extent and in Suzuka he was almost trying to overcompensate by focusing on staying out of trouble, which in the last race had the opposite effect."
- Sergio Perez