Lewis Hamilton said he is going to work hard to understand why he has started losing out to team-mate Nico Rosberg in qualifying.
Rosberg won the Brazilian Grand Prix to take his second victory in a row, following his fifth consecutive pole.
Hamilton began the year with 11 poles in 12 races, seven of which he won.
"Nico drove a fantastic race. Nico has been doing a fantastic job in qualifying. I have to think how things have changed," Hamilton said.
The Briton tied up his third world title two races ago, but since then Rosberg has wrested back the momentum and Hamilton said he felt it may be related to a change to the car Mercedes made at the Singapore Grand Prix in September.
"Since Singapore, there have been some changes to our car which seem to have shifted the direction of the ways [the respective fortunes of himself and Rosberg], so I need to figure out why that is and how I can get back on it.
"I have to try and improve in qualifying. Something has shifted in the car, I guess I have been a little bit less comfortable with it.
"I have only just noticed that is the only thing that has changed since things have changed, so maybe I need to go and do some studying and see what I can do to change that."
Hamilton said he would be aiming to sort the problem out before the final race of the season in Abu Dhabi from 27-29 November.
"These next months are going to be really important and going to Abu Dhabi trying to get back on top of that," he said.
"I have not lost any pace. I will be working hard for the next couple of weeks."
Hamilton did not say what the change was, and Mercedes executive director (technical) Paddy Lowe said he did not know what the driver could be referring to.
Hamilton appeared faster than Rosberg during the race at Interlagos but was unable to pass and said he had no problem with Mercedes' refusal to let him try a different strategy.
"I felt really good," he said. "I was pushing like crazy, I had nothing left.
"Unfortunately these tyres run out, don't allow you to race to the end.
"If only you could see the air around us you could see the dirty air and I end up losing the downforce and damaging my tyres even more.
"I was looking for other options but the priority for the team is to get a one-two and do pretty much the same thing."
Hamilton said he would like to have taken a risk and switched strategies but Mercedes F1 boss Toto Wolff said that at the time Hamilton wanted to do that, it would have compromised his race and put his second place at risk.
Wolff said the team would not change their approach.
"If the driver in the car starts to choose the strategy he is going to lose every single race because it is not an instinct-driven decision," Wolff said.
"Your instinct might be right sometimes but if you do not have the full set of data you are going to get the majority of your races wrong.
"It is sometimes difficult to manage letting the two fight with each other and now you could even say let's take it one step further and also let the strategists fight with each other.
"But this is not where we want to get.
"Controversy within the team is detrimental and we have kept the team together because the team comes first and so, from a fans' standpoint, I can understand, but from a team's stand-point we are not going to change."