The Formula One leader was outpaced by Mercedes teammate Valtteri Bottas in both practice sessions. After finishing fourth in the timesheets in the morning Hamilton did post the second fastest time in the afternoon, 0.069 seconds behind Bottas.
"It's been quite windy, quite gusty out there, so it hasn't been the easiest of days, but we were up there nonetheless, and it looks like we'll be in the fight," Hamilton said.
"I was struggling with the rear end and went off a few times, but Valtteri seemed much more comfortable in the car, so we are going to dig deep tonight trying to figure out what the issue is and how we can solve it for (Saturday's qualifying)."
In front of his home fans, Hamilton looked well placed to beat Bottas before having to abort a lap.
"The asphalt is very smooth which makes it tricky to get the tires to work, they're in and out of the window," Hamilton said, "and the gusty winds didn't make it easy."
Hamilton holds a 31-point lead over second-placed Bottas in his F1 title defense after nine races, but the Finnish driver felt far more confident on Friday.
"I've had a good day from the get-go, both in terms of my own performance and the set-up of the car," Bottas said. "It's always a nice feeling when you start a weekend like that. The track is less bumpy than last year which is nice. They did a good job on the asphalt and it was very enjoyable to drive.
"The new surface is quite grippy, but sometimes you can lose the grip very suddenly on new tarmac. The car seems quite well-balanced."
There could be a strong challenge from the Ferrari duo of Charles Leclerc and Sebastian Vettel, who were behind both Mercedes drivers in the second practice.
Leclerc was two tenths of a second off Bottas, and Vettel was less than a second adrift.
Red Bull driver Pierre Gasly, who topped the timesheets in first practice, dropped to fifth in the afternoon.
In the morning, Romain Grosjean crashed his Haas in the pit lane, spinning out of control and losing his front wing. A hydraulic leak kept Grosjean out of 40 minutes of the second practice on a day to forget for the Swiss driver.