Alonso secured sixth on the grid for last week’s Bahrain Grand Prix, but slipped back to a distant ninth place in the race.
He has again qualified well in Jeddah, earning fourth on a day that regular Ferrari driver Carlos Sainz was absent, and Mercedes struggled with bouncing.
“We are surprised, we still surprised about the performance of this car over one lap,” he told Autosport.
“I think it's not our natural position to be in the second row of the grid. We saw in Bahrain we were very strong in free practice and qualifying and then, in the race, we fell back to our more natural position - the fifth-fastest team behind McLaren, Ferrari, Red Bull and Mercedes. This was more or less the same story.
“We are ultra-competitive over one lap, and the car is responding well. But we are still very concerned about the race.”
Alonso added that, after his struggles in the Bahrain race, the team had attempted to address the issue for this weekend.
“In Bahrain, we were definitely faster over one lap comparing the long-run pace,” he said. “Here, it seems that we were faster on Friday on new tyres than on the long-run pace, so there is a trend.
Source: Autosport