Sebastien Buemi's hopes of remaining on the F1 grid next season would appear to hinge on a strong end to the 2011 campaign after Toro Rosso team boss Franz Tost insisted that three years was long enough to judge if a driver has what to takes to be a success in the sport.

Buemi is in his third season with the team having made his debut back in 2009 and is viewed by many as being at risk of losing his seat for 2012 to Daniel Ricciardo, who has been placed in a race seat with Hispania by Red Bull to better prepare him for the future.

Speaking in an interview with the official F1 website, Tost again insisted that the team wouldn't make a decision on its drivers for 2012 until the current season has come to an end, although his comments that a driver should have shown their potential within three years would appear to put the pressure firmly on Buemi to get the results before the season draws to a close.

"They [Buemi and team-mate Jaime Alguersuari] are moving forward - that was clearly visible in the last couple of races, with the last race seeing both of them in the points - so let's wait and see how the second half of the season works out," he said. "Then at the end of the year we will sit together with Red Bull to discuss who will sit in our cars in 2012."

"If you are not sure after three years whether he's [a young driver] going to make it, I would bluntly say forget him, period. Three years - why? Because this is the time a driver needs today in Formula One to develop from a rookie into a calculable factor in the team. There is no testing anymore, so a driver who has made it into F1 faces a completely new world. At best he knows all the European tracks from GP2, but Formula One is so different to anything he's ever experienced.

"There is the technical aspect, the significantly larger team, the many new overseas tracks, the interaction with the media, the marketing side. All of that you don't learn overnight. And then he has to come to terms with the fact of being nowhere on the grid. Most of these youngsters have been hugely successful in lower series, believing that the front row is their rightful place. Finding out that a Formula One life can be so different is something that is hard to swallow."

Tost added that both drivers were doing a good job for the team, which currently sits eighth in the championship standings, but said he was looking forward to working with the next generation of Red Bull drivers as they work their way through the motorsport ranks.

"I think Sebastien and Jaime are doing a good job and I am also really looking forward to working together with the other Red Bull youngsters, Daniel Ricciardo and Jean-Eric Vergne," he said. "Both have done the young drivers' days with Toro Rosso last year in Abu Dhabi and Daniel was our third man before he got the opportunity to race for HRT. I expect him to best Liuzzi after not more than three or four races."