Romain Grosjean believes his former Lotus team-mate Kimi Raikkonen is struggling in Formula 1 this year because the cars do not suit his driving style.
Grosjean and Raikkonen were team-mates at Lotus for two years before Raikkonen joined Fernando Alonso at Ferrari for this season.
Raikkonen has endured a difficult start to his second spell at the Scuderia, and languishes 12th in the points having failed to finish ahead of Alonso across the first 11 races of 2014.
Grosjean has been team-mate to both Ferrari drivers and he reckons 2007 world champion Raikkonen is suffering more than most from changes to F1 cars brought about by the radical shift in regulations for this year.
"I know what he doesn't like and I think this year's cars don't suit him very well," Grosjean said.
"He needs a good front-end and that car doesn't give this feeling.
"It's hard to explain, but it can change your confidence."
Grosjean was also briefly a team-mate to Alonso when he made his F1 debut with Renault in 2009 - the season before the double world champion moved to Ferrari.
The Franco-Swiss driver says he did not know before the start of this campaign which of the two would be stronger at Maranello.
"I think they are both very strong," Grosjean added.
"When I was with Fernando I was inexperienced and the car wasn't the best.
"He could always get on top of what he had and get 100 per cent from the car, even though he had to drive three different styles in the lap, which is very good.
"Kimi was quick, consistent, and capable of building his weekend as well.
"It was nice for me to have him on board, even if the chat wasn't very big!
"They were different, [but] I was in different stages of my career [with each one].
"To be fair, at the beginning of this year I didn't know which one was going to be the best. To me, they are both very strong."