Yamaha said Ben Spies' poor performance in the Qatar Grand Prix was caused by a severe chatter issue on his bike.
The American tumbled from fourth on the grid to 11th at the finish - just 1.1 seconds ahead of Colin Edwards' CRT Forward Suter-BMW, while Jorge Lorenzo took the sister works Yamaha to victory.
Team director Massimo Meregalli said the problem had manifested itself without warning in the warm-up.
"The chatter suddenly appeared on Ben's bike in warm-up and we couldn't solve it before the race," said Meregalli.
"We're not sure why it was yet but the engineers will work on it and we will try to ensure we have the problem solved by Jerez."
Spies had crashed twice in the build-up to the race, and admitted there was little comfort he could take from the Losail weekend - describing his grand prix performance as "pathetic" in an interview with the official MotoGP website.
"I tested my airbag twice this weekend; good to know it works well..." Spies joked. "We'll go back to Jerez now and hopefully have the bike issue sorted.
"It was good that Jorge won, we can see the Yamaha is going well, we just had a big problem with chatter so we have to work out what it was."