Ben Spies was struck down with a nerve problem in his chest that left the Ignite Pramac Ducati rider pondering whether or not to retire from the Austin MotoGP.
Spies gritted his teeth and eventually finished in 13th place, but the American rider was bitterly disappointed with the result at his home race at the Circuit of the Americas.
He felt a twinge in his chest during morning warm-up and sought medical treatment before taking his position on the grid for the race.
Spies explained: “I had a little problem with a nerve in my chest for some reason.
“I don't know if it's from overcompensating for my shoulder problem, which is actually getting a lot better compared to Qatar.
“That said, two laps before the end of the warm-up, I had a twinge in my chest,” he added.
“It was like a knife, so we went to the clinic and they worked on me a lot and got me ready for the race.
“I tried as hard as I could during the race, but it wasn't enough.
“At eight laps to go, it was either come in or salvage whatever points we could.”
Spies has pledged to 'work harder' with the bike as he attempts to improve his results over the coming races.
“We need to work harder and get back to 100% and just keep working with the bike,” he said.
“I'm more disappointed for the team, friends, family, fans, Ducati, and Ignite Pramac, because they deserve better.”
Francesco Guidotti, Pramac Racing team manager, said he expects Spies and Andrea Iannone – who finished tenth in Texas – to be closer to the leading group at the European tracks.
“These two rounds took place on two really tricky circuits, at a time when our riders are in less-than perfect physical condition, so the gap to the top riders is larger than it could be in a normal situation,” he said.
“We look forward to the European circuits, which both riders already know, and for which they'll have had a chance to rest and recover.
“We expect to finish closer to the lead group.”