Championship leader Lewis Hamilton says Mercedes is "working hard" to catch up with Ferrari.
Although he and Mercedes could mathematically wrap up the championships with a full four races to spare this weekend at Suzuka, Hamilton is concerned about Ferrari's latest leap forward.
"Ferrari has always had a good overall package," he told the German broadcaster RTL.
"But now they have changed something about the engine to make it better than all the others. It's making a big difference."
Heading into Suzuka, team boss Toto Wolff said Mercedes has a "minor" update for the Japanese GP. Technical sources at Suzuka say it is in the area of the bargeboards and front wing.
"We're working hard to figure out how to get faster," Hamilton confirmed.
"At the last race, we were four tenths slower in qualifying because they were seven tenths faster on the straight.
"I cannot push down on the gas pedal any harder, so we need to find out how to make more time up in the corners, reduce drag and get more power."body check tags ::