A week after his near-perfect triumph in Australia, Button was left apologising to McLaren following Sunday's race at Sepang.
The 32-year-old Briton finished 14th in Malaysia after a collision with the HRT of Narain Karthikeyan.
After going into the race with a seven-point cushion over the field, Button now trails Fernando Alonso by 10 following the double world champion's win.
Button, however, does not believe the Spaniard - in a so-far underperforming Ferrari - is a realistic title threat this season.
"Even after such a bad race - and that's hopefully my bad race for the year gone - I'm still only 10 points off the lead, and that's Alonso in a Ferrari. That's not the worry," Button said.
"I'm also only five points behind Lewis, who is the guy in a competitive car, so (it's) still not bad considering the day I had. Lewis is definitely my main rival, and you have to say the Red Bulls as well.
"Those are the guys I still think are the main ones at this point in the season, and will be for quite a few races.
Worried
"The Mercedes show signs of speed in qualifying, and we'll have to see what they can do in a nice dry race, and see where we stand compared to them. But the team we should still be worried about the most are Red Bull."
Even though Alonso himself insisted his victory meant nothing had changed within Ferrari given the overall uncompetitive nature of their car, McLaren team principal Martin Whitmarsh is refusing to write them off.
"You can never underestimate Ferrari, but it was a turn-up for the books they were able to win," said Whitmarsh.
Asked if he was worried that Ferrari would emerge in Barcelona with a decent car - the Spanish Grand Prix is pinpointed as the race when teams deliver a major upgrade - Whitmarsh replied: "You always are.
"When you are trying to win a world championship you are always worried that at every race weekend you go to someone will deliver a bit more performance.
"If you're honest about it, at the back of your mind, you are wondering whether anyone turns up with a eureka moment and they overhaul you.
"But it's a long, long championship ahead, and although we're not in bad shape, nothing is taken for granted here.
"No one, with confidence, can predict the outcome of this year's world championship, and that's how it should be."
