Spurs dropped to fourth in the Barclays Premier League after a lacklustre display at White Hart Lane against Fulham was settled by a goal from former striker Dimitar Berbatov.
It was a second straight league defeat, and allowed rivals Arsenal to close the gap to just four points, with a match in hand and far superior goal difference.
The Iceland midfielder, though, claims Spurs must concentrate on getting themselves back in form over the final eight league games - and then it will not matter what any other sides do.
"We just need to pick ourselves up, stay together and perform well until the end of the season," said Sigurdsson, who started his second match of the week after their Europa League tie at Inter Milan.
"It (a top-four finish) is in our hands and we are in a good position to make sure we get the Champions League spot.
"We showed during the season that we are more than capable.
"Even though (we've had) a couple of bad results, we won't start doubting ourselves.
"It's down to us now and we have just got to make sure we are playing the way we've been playing throughout the season."