"It feels like you have to slow down too much now, to the point that it's a bit boring," Hamilton said, adding that he expected a "tough day" during the last practice and the qualifying session on Saturday.
The British driver, who crashed during qualifying a week ago for the German Grand Prix in Hockenheim due to brake failure, could be heard complaining about the brakes again during practice over the team radio. Later, however, he did not seem too concerned.
"I just had some brake settings that weren't great," Hamilton said after the second practice session. "This is a continuing issue we need to work on."
Hamilton won four of the first five races of the season, later adding a fifth in at the British Grand Prix. He has 176 points, 14 behind Rosberg and 70 ahead of Ricciardo, the only other winner in 2014.