Team-mate Nico Rosberg was eight fastest in practice today, half-a-second off the pace, with Hamilton 10th overall 0.822s down.
The 2008 world champion is unsure about the direction the team has taken with the setup so far this weekend.
"We're working as hard as we can and we just need to find some more time from somewhere," said Hamilton.
"I don't really know where we are losing it.
"They have changed the car this weekend, changed the settings for what they think the track needs but I'm not convinced it is the right way to go.
"I don't know if they are right or wrong, but we were struggling for pace today. But I am sure we will find it."
Rosberg said he was struggling with understeer in his car as a result of a set-up aimed at making the rear tyres last longer.
"Today we had a bit too much understeer, but then again you need to have understeer in the car because if you load the front tyres more, it helps take some load off the rear tyres," he said.
"This track is really demanding on the rear tyres, and that's the key to winning races here, take care of the rear tyres better. It's always a compromise."
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