Hamilton slumps to 18th in Melbourne practice as changes backfire
The British star finished ninth in the first practice for the Australian Grand Prix, but slumped to 18th in the second session to be 1.5 seconds adrift of Ferrari pacesetter Charles Leclerc.
"I obviously don't feel great. We had one of the worst sessions I've probably had for a long time," said Hamilton, who is leaving at the end of the season to join Ferrari.
Mercedes changed his car's setup between FP1 and FP2 in a bid to improve the high-speed cornering problems and bouncing that dogged him in Saudi Arabia.
But Hamilton said it made matters worse.
"We began the day on the front foot and in FP1, the car generally felt good. The first run was actually the best the car has felt so far this year," he said.
"To continue our learning, we made some big changes into FP2 and unfortunately, that made the car worse.
"It was tough but there are positives we can take from the first session. We will be working hard overnight to make improvements ahead of tomorrow."
Teammate George Russell fared better, finishing sixth, and felt he could have made the top three.
"I was on for a really good lap on my last push on the soft tyre, but just ran wide in the last two corners and picked up some minor damage to my front wing," he said.
"Without that, I think we would have finished the session P3.
"Every single lap is so valuable as you learn more about the car and try to get it into the sweet spot," he added.