Sergio Perez will start the Spanish GP from eighth place on the grid, having had a subdued qualifying session that included a spin during his first flying lap in Q3.
The Mexican's poor showing might now be explained, as he has confirmed that he experienced quite serious left shoulder pain and dizziness during the qualifying hour.
"Yeah, I did struggle, I didn't feel 100% with myself today, you know, bit of an issue with my shoulder through qualifying," Perez told media, including RacingNews365.com.
"I was just feeling bad all the way through it. But spoken to the team, we will review everything and we should be back to 100% tomorrow."
Asked whether it was something to do with his seat position and whether he had exerted himself in a particularly strenuous way, Perez said he didn't feel there was anything in particular that could have caused it.
"I don't think it's something I've done with the car," he explained.
"We don't know 100% what it is, but we're pretty confident that we can be back to form for tomorrow.
"It was just getting worse and worse as qualifying developed. I struggled with a bit more with it. But yeah, as I say, it should be fine tomorrow."