Alonso completed five laps in the new MCL33 car before the right-rear wheel came off and he spun into the gravel.
But he claims it was a minor incident and that a number of rival cars are in worse shape behind closed doors.
Speaking about the crash, Alonso said: “That it was a good day for you guys [the media]!
“It was a very, very small problem but very graphic and very obvious because a car in the gravel is a big thing.
“There are six teams in the garage with the door closed with the car in pieces, but no one sees – there are no pictures of that.
“There are a lot of teams in trouble – and big trouble – and for us with a wheelnut it will make the big thing of the day.”
Despite the blip, Alonso recorded the seventh fastest time of the day and clocked up a total of 51 laps.
He was initially ranked fifth but his hottest lap was scrubbed off for cutting the final chicane.
McLaren are hoping their new partnership with Renault will improve their performance and Alonso was pleased with their first day of testing.
“So far, so good,” he said. “Obviously very early days, but the car and engine was running fine.
“I know a lot of people from Renault from my past. I know 80 per cent of people in the garage and how they work and how much attention they play to driveability and the performance of the engine.
“Every run was a nice chat with them, in Navarra at the filming day and also here. It was running very smoothly. There are a few things we are trying to change and adapt like every new car. But on the engine side extremely happy and there is huge potential in the McLaren-Renault team.”