Bruno Senna has played down his chances of standing in for the injured Robert Kubica at Lotus Renault GP this season, after claiming that rival Nick Heidfeld is much better placed to do the job.

The Brazilian, who was added to the team's five-strong reserve and testing roster, has just one year of F1 behind him, and with the tail-end Hispania Racing team at that, and conceded that Heidfeld, who joined him in testing the promising R31 in Jerez last week, brought more to the team at this point in time.

Senna set the fifth fastest time on the final day of running in southern Spain, and went quicker than the already confirmed Vitaly Petrov had managed during two days on track earlier in the week, but accepted that he probably does not have the level of experience to compete with F1 veteran Heidfeld as Lotus Renault attempts to get its car on a par with the likes of Red Bull, McLaren and Ferrari. The German set the pace on day three of the test, while Senna was prevented from chasing a better mark by rain late on Sunday.

"I only had one day in the car and it was good but, for preparation, you need much more than that - they need a driver that's ready to do it," the Brazilian, who was getting his first taste of the Pirelli tyres, KERS and adjustable rear wing that feature in F1 in 2011, admitted to Britain's Daily Telegraph, "It wasn't a trial. In unfortunate circumstances, I was given a great opportunity to drive the car and do some work for the team.

"Considering that I've only been here for three weeks, it's a great shot for getting some experience with the car and the team. It was only the second test I have had in a F1 car - ever. But the team knows what they need and it's up to them what they do."

Heidfeld has also refused to accept that he is a shoo-in for the drive, which could extend for the entire season despite Kubica vowing to return before the end of the campaign. The Pole suffered serious hand, arm and leg injuries in an accident on the Ronda di Andora Rally in Italy last weekend, and has undergone two lengthy operations to reset fractures that many felt could end his career.

There is one further F1 test in Europe before the circus heads to Bahrain for the opening round, which will be preceded by another session on the desert circuit at Sakhir. With the line-up expected to be settled by the time the teams arrive at BIC, it is unclear whether Force India refugee Tonio Liuzzi - the only other driver suggested to be in the frame to replace Kubica - will get a chance to prove his merit in the R31.

Team boss Eric Boullier has admitted to being impressed with Heidfeld's efforts on Saturday, and it may be that the German, who revealed that he was considering switching to the DTM as well as chasing F1 reserve roles for 2011, will be given as much time as possible to help hone the car before its race debut.