Button finished sixth in the 2006 drivers' standing for Honda
Former Formula One world champion Damon Hill has warned Jenson Button he might have to quit his Honda team if he wants to win the drivers' title.
Button complained about a lack of pace in pre-season testing and Hill believes Honda may never match his ambitions.
"If Jenson is serious about becoming world champion then he has to get himself in a car that is a championship contender," Hill told BBC Sport.
"If Honda don't turn it around then Jenson's hopes will be hurt."
Button took his maiden victory in 2006 at the Hungarian Grand Prix - in his 113th race - but Hill fears Honda have failed to build on their breakthrough over the winter.
The new RA107 car has struggled for speed in testing and the Englishman found himself 14th on the timesheets during the final session in Bahrain with team-mate Rubens Barrichello sixth.
The indications ahead of the opening Australian Grand Prix on 18 March are that Ferrari, McLaren, Renault and possibly BMW Sauber will be battling it out for the podium places - with Honda lagging some way behind.
Jenson was the top Briton but now Lewis Hamilton has arrived on the scene we'll have to see how things stand
1996 world champion
Hill said: "There are still questions over Honda's ability to find that 5% which makes the difference between a Renault, Ferrari and McLaren, and a team like Honda.
"When the car was looking good last season they only managed to win one race and you have to go forward from that.
"But that's the hard bit, the push to the summit. It seems that Jenson has found himself with a team that are finding that final push very hard."
Button joined BAR, who were bought out by Honda before the 2006 season, in 2003 after Renault chief Flavio Briatore decided to promote test driver Fernando Alonso.
But in an injudicious move, the Briton signed a pre-contract with Williams for 2006 only to change his mind and decide to stay with BAR-Honda.
The resulting legal wrangle saw the team come to a financial settlement with Williams and tie Button to a multi-year contract.
And Hill says that result may have ultimately cost the 27-year-old a genuine shot at the title.
"Jenson cannot afford too many more seasons before it all starts to look like it has passed him by," said Hill.
Hamilton could threaten Button as the top British driver in 2007
"As a driver he has got a clock that's ticking but he has committed himself to the team and the team are committed to him - so he has a real issue now.
"He mustn't get frustrated but I've heard that he has been very vociferous in private that the car is still not the car that will win a championship yet."
Hill, the last Briton to win the Formula One crown in 1996 with Williams, believes Button will come under increased pressure this season from English newcomer Lewis Hamilton.
Hamilton makes his debut with McLaren, who are expected to be competitive, especially with world champion Alonso as lead driver.
And Hill says though Hamilton, 22, is a novice he could be a real threat to Button - and his world title ambitions.
"Jenson was the top Briton but now Lewis has arrived on the scene we'll have to see how things stand at the end of this season," said Hill.
"Jenson or Lewis could both be the next British world champion but while Jenson has the edge of experience, it is Lewis who is working with the better equipment."