Bruno Senna remains hopeful he will be on the 2013 Formula 1 grid

The Brazilian has been replaced by Finnish driver Valtteri Bottas, who will partner Pastor Maldonado from the 2013 season.

Senna has been in talks with Caterham and Force India and is believed to be still in the running for a seat with both teams.

AUTOSPORT understands that Senna tested a DTM car for Mercedes at Estoril last week, but he says he is still working hard to secure a slot for what would be his second full season in F1.

"You're never relaxed until you have a nice signed contract, but we're working very hard," Senna told AUTOSPORT. "Chris [Goodwin, manager] is a busy little bee. He's been doing his job very well.

"Hopefully before the end of the year we'll have a nice clear path to follow."

Senna insisted that having to make way for Bottas in 15 Friday practice sessions during the season made his year more difficult.

The Brazilian reckons he still did a good job considering his relative lack of experience.

"It's a tough world championship," he added. "This has probably been the toughest Formula 1 world championship in many years. I think that coming into it as my first real year in Formula 1 was already a challenge.

"And then missing practice sessions all over the season, probably missing about 30 per cent of all the practice sessions of the year, is a lot of practice missed.

"That probably puts you in a position where you shouldn't be at the start, only by a couple of tenths sometimes.

"It's made my year much more difficult. But still I've learned a lot. It's been a very big learning curve for me, and a very good one."