The Belgium international centre-back says he will not make any decision until after the World Cup.
But Vertonghen, who joined Spurs from Ajax in a £9.6m deal in 2012, admits that he cannot be sure he will still be at White Hart Lane at the start of next season if the north Londoners fail to finish in the top four.
"Those are always difficult questions," Vertonghen, who signed a four-year deal with the club when he joined, told the Evening Standard.
"What I want is to be playing in the Champions League with Tottenham, so I hope we get in this year.
"Do I have a decision to make if we don't? I can't say anything about that. Let's see after the end of the season, after the World Cup."
The 1-0 defeat to Norwich on Sunday left Spurs trailing six points behind Liverpool, who occupy fourth place.
Tim Sherwood's men will go to Anfield at the end of March and they also have matches with Chelsea and Arsenal before the end of the season.
Spurs have taken just one point off the current top four teams all season, and Vertonghen admits they have to change that form if they want to qualify for the Champions League.
"We'll need quite a lot of points from those games," he said. "Chelsea and Arsenal are still competing for important things so they will be tough games but we've showed we can beat good teams and we have to step up.
"Mentally, we're strong enough. Maybe we're one of the best teams mentally because we support each other all the time but we need to get things right on the pitch.
"Against Norwich, it was just not good enough. We need to improve the level of our game to compete for the top places."