Romain Grosjean's start to the Spanish Grand Prix got off to a dramatic 'bang' when his Lotus' engine cover exploded down the home straight.

The Frenchman was starting his fast lap when the panels ripped off and shattered, prompting the session to be briefly red flagged as the debris was cleared.

Putting the issue down to a likely small broken part that was then exacerbated by the speed he was doing, Grosjean admits there was more damage than he expected.

It's just a small part of carbon that probably broke," he said. "And the air went into the engine cover and it just made a big explosion. I saw it in the mirror. For some reason I was watching in the mirror at that time, so I saw it live.

"I went to the radio and said 'I think I've broken something'. I thought it was a small panel initially. I drove on the lap quite slowly but the car was undriveable. I came back to the box and saw the TV footage. It's more than a small part."

The Frenchman was 12th quickest in second free practice having sat out FP1 to make way for test driver Jolyon Palmer.