Ben Spies says visibility issues caused by water leaking into his helmet were the chief culprit behind his struggles at Le Mans.
In contrast to Yamaha team-mate Jorge Lorenzo, who dominated from the front, Spies fared miserably, dropping down the grid after the rear of his bike got loose at the start.
He fought back to get as high as 13th, but could not break free of the surrounding CRT bikes and eventually brought his race to an effective close - even though he was able to return - by heading into the pits.
The Texan said visibility issues were to blame for his slump. He has just one top 10 finish to his credit this season, an eighth in the previous race at Estoril.
"That was a rough race," Spies conceded. "We actually got off to a good start at the beginning then had a very big moment on the line.
"Something happened because then I had quite a lot of water coming in through my helmet and couldn't see much on the first five laps. I hoped it would get better but I couldn't see anything and decided to come in because I need to see where I am going.
"I knew the race was gone by then so went back out to try and get some data and get better working with the bike in the rain. Circumstances meant it wasn't a good day."
After hailing Lorenzo's 'incredible' ride, team director Massimo Meregalli said he expected Spies to bounce back at Barcelona.
"We were expecting a different race but unfortunately this bad luck doesn't want to disappear," Meregalli said. "We're looking forward to Barcelona, we won't give up and we will get back up to where we belong with Ben."