Lotus team principal Eric Boullier has called on driver Romain Grosjean to "stand up" and take the reins when Kimi Raikkonen leaves at the end of the season.

Raikkonen will return to Ferrari and team up with Fernando Alonso for the 2014 Formula 1 campaign, leaving Grosjean the chance to step out of the Finnish driver's shadow.

"When you are a young driver and you are racing against Kimi and obviously the personality and charisma and results, it is good to grow up," Boullier told Autosport.

"But to stand up is more difficult, so now Kimi is leaving it is the right opportunity for Romain to show us what he can do."

Grosjean is almost 100 points behind Raikkonen this season.