Pedro de la Rosa believes reaching the final qualifying segment will be challenging, despite admitting he was happy with his day's work on Friday.
The Sauber driver finished the day as tenth quickest, but he believes the top eight positions belong to Red Bull, Ferrari, McLaren and Mercedes.
And with Force India having shown strong form today, de la Rosa believes reaching Q3 will be tall order.
"Reaching Q3 will be hard," de la Rosa told Spanish reporters. "There are eight positions which are already fixed and then there are sixth or eight cars fighting for the other two.
"And on this track Force India will be a very though rival to enter. Probably they can make it to Q3.
"But there's still time to improve. I'm going to improve too. You can't underestimate how rusty I am. I have experience but it's been a long time since I race here in Bahrain. I know I'll be better tomorrow."
The Spanish driver said he was pleased with his day after improving his car during the sessions, but he claims there is still more to come.
"It's been interesting, especially because we found ourselves with a difficult track," he added. "The new section is very bumpy with lots of spinning and we had to change the car's set-up during the sessions.
"In the end the car was a lot better, but we still need to improve quite a bit for tomorrow if we want to score. But in general I'm happy because we managed to improve the car throughout the day."
Team-mate Kamui Kobayashi posted the 11th fastest time of the day, the Japanese admitting the his car was particularly hard in the new section of the track.
"After we lost some track time this morning because of a puncture, we were able to complete our programme in the afternoon," Kobayashi said. "We now have to look at the set-up again.
"I have the impression the bumpy new infield is pretty difficult for us, but we will work on that. I have no complaints about the heat either, as I definitely prefer it compared to the winter in Europe."