Spurs missed the chance to boost their top four hopes after losing 4-0 to Chelsea last weekend to leave them four points behind Manchester City, having played three games more than Manuel Pellegrini's men.
Vertonghen accepts it is going to be a massive ask for Tottenham to finish in the top four with just nine games left this season.
"Is it over and out for the Champions League now? I'll never say that, but it's going to be hard," Vertonghen said.
Vertonghen was at fault for Chelsea's crucial opening goal at Stamford Bridge when he slipped and in trying to recover his pass went straight to Samuel Eto'o to allow him to score past Hugo Lloris.
"I slipped away and thought Schurrle could take the ball," added Vertonghen. "That's why I tried to slide the ball to the goalkeeper.
"But accidentally, it seemed to be the perfect assist for Eto'o. It was the beginning of a hard night."
Vertonghen was forced to play at left-back at Chelsea due to an injury to Danny Rose and asked about Tim Sherwood's decision to move him from central defence to full-back the Belgian noted: "I was told on Friday. The coach decided to use this tactic, so I listened and did my best."