The 42-year-old Aston Martin driver said he had not expected to be so competitive, but added that he hoped he might be in contention to repeat his surprise podium finish last year.
The two-time world champion on Wednesday said he would decide his future after the "first few weeks or races" because of the demands of this year's unprecedented 24-race calendar.
"Well, first of all, I need to decide if I want to keep racing and that will be the first thing that I need to decide - in a few weeks or a few races," he said when asked if he was interested in joining Mercedes to succeed Lewis Hamilton next year.
"I feel great now, but I know it's a demanding calendar and in 2026 there are a different set of regulations as well, which maybe are tempting or maybe not, I don’t know."
After qualifying, however, the evergreen Spaniard, who has adopted a new diet and fitness schedule, said: "I feel great. I didn't expect we would be that competitive, to be honest.
"Winter testing was ok, but I think we are not in the pace of the leaders.
"Free practice was competitive, but we found also last year that sometimes in free practice we are running in a different engine mode and in qualifying everything is a bit more realistic.
"It's going to be difficult in the race, very tight in a group which will damage the tyres even more when you are in traffic. So, I think it's going to be a question mark for everyone. Let’s see."
He made no further comments about his future, having declared that 24 races is "well over the limit".
"When I started, we had 16 races, then it was 18 and then I think Liberty (the American owners of F1) came and we had 20 in a season and that was the limit, 20 races, but now we are up to 24.
"It isn’t sustainable for the future, I think, not for anyone."
