Hamilton finished fifth and seventh respectively in the first two practice sessions in Mexico.
The Brit needs to finish no lower than seventh this weekend if he is to win his fifth world title.
Red Bull pair Max Verstappen and Daniel Ricciardo topped the leaderboard in practice.
Hamilton’s closest title rival Sebastian Vettel finished no higher than fourth in either session.
But Lewis Hamilton is concerned about the difference in performance between his Mercedes car and the Red Bull machines.
“Red Bull seem out of our reach at the moment, Ferrari are right there with us, but we’re here to try and compete, so we will do the best we can to have a real race,” Hamilton said.
“We’ve got some ground to catch up on, so we’re now going to go through everything in the debrief and look at all the details to find some answers.
“On the long run I think I was right there with Sebastian [Vettel]’s times, so we’ll have a bit of a battle.
“The car was good in some places, but not so good in others,” Hamilton said after practice.
“It’s not about one particular area; there are lots of different things that we can improve.
“It was difficult with the high track temperatures, which were melting and graining the tyres, but a lot of people were experiencing that today.”
Mercedes technical director James Allison explained there were more issues with the car than just the tyres.
“We were overheating the power unit in a number of areas today, and that meant we had to protect against this by turning it down as a precaution,” he said.
“With a bit luck, and no little hard work, we can get ourselves into better shape tomorrow and on Sunday, when conditions are also forecast to be cooler.”