di Grassi admits: F1 hopes rest on Piquet future.

Despite a hugely impressive GP2 Series campaign, Renault test driver Lucas di Grassi has admitted that his only chance of graduating to a Formula 1 race seat with the R?gie next year is if Nelsinho Piquet is no longer there.

di Grassi began 2008 purely as a test driver for the French concern - alongside fellow GP2 Series race-winner and Asia Series Champion Romain Grosjean - but after missing the first six GP2 races elected to return to F1's feeder category with Campos Grand Prix, a decision that would pay off richly.

Having finished as runner-up to Timo Glock in the championship in 2007, the Brazilian produced a stunning late-season run - with three victories and three second places from just 14 outings - to clinch third position in the final rankings twelve months on, a single marker adrift of second-placed Bruno Senna and only 13 points shy of eventual champion Giorgio Pantano, who tellingly had notched up more than twice that amount in the three rounds di Grassi missed.

"After two or three races you get the training back, but at the beginning of the year it was very hard for him [Piquet]," the S?o Paulista explained to Italian website 422race.com on why he chose to step back to GP2 again in June, pointing to the example of his under-fire countryman, who found himself somewhat ill-prepared for his F1 debut after simply testing and not racing in 2007.

"I think to be fast is one thing, but races are races. You have to work on both sides. We racing drivers want to race, not just do a fast lap in testing - that's not how we work.

"Moreover, this year the third driver was used so little, almost nothing, just six or seven days a year. For me it was very difficult to stay two months without driving and then do a good test. It was better to stay fit driving GP2, which is the closest car to Formula 1, and then go fast with the F1 car by being more prepared.

"Secondly, I was invited to race for Campos, which is a team which wasn't going so well but in which I knew well what I could do. I decided to come back into GP2 to train for F1 and also to win races, show to be the best driver of the category and deserve a promotion."

That the Renault Development Driver has undoubtedly done, and though openings on the 2009 grand prix grid are proving to be few and far between for GP2's leading lights, di Grassi knows that Renault remains considerably his best chance - even if such a progression does, he acknowledges, depend on one key factor.

"If [Fernando] Alonso goes away, in my opinion it's difficult for the team to choose two inexperienced drivers - Nelsinho as a first driver and a rookie alongside him," the 24-year-old acknowledged. "It's impossible for a competitive team to make such a choice.

"If Nelson goes away, maybe I'll have a possibility. Now we have to wait for Fernando and Nelson to decide. It doesn't depend on me, but on Flavio [Briatore - Renault managing director] and on the Renault team.

"I want to do my job, which is to win races and do well in testing, and then we will see. Renault still hasn't told me anything. They are happy about my GP2 results, much more than last year, but still they haven't spoken about next year."

di Grassi tested for the Enstone-based outfit at Jerez in southern Spain earlier this month, impressively lapping fourth-quickest of the 16 drivers present over the four days, less than a second off the leading time.

The security of Piquet's seat at the team has been the subject of uncertainty for much of the season, with suggestions the underperforming 23-year-old was to be replaced after just the opening four races. The 2006 GP2 Series Vice-Champion failed to aid his cause by crashing out of the inaugural Singapore Grand Prix last weekend, even if his accident ironically probably enabled team-mate Alonso to win the race.