The Spurs defender is looking forward to Sunday's live Sky Sports clash at White Hart Lane, when seventh will host eighth.
City have struggled on their domestic travels so far this season, losing at Cardiff, Aston Villa, Chelsea and Sunderland.
However, Spurs have suffered surprise home defeats to West Ham and Newcastle so the weekend duel looks hard to call.
"It's really crazy," Vertonghen told Sky Sports News.
"I think if we'd won against Newcastle, we'd be joint second now - but we're seventh.
"It's unbelievable how we play City and United next. It's very hard this year. (Vincent) Kompany already said it will be the toughest league in years to finish top. We have to be at our best to finish in the top four."
Despite City's slip-ups away from the Etihad this season, Vertonghen understands why Manuel Pellegrini's men are favoured by the bookies at this moment in time.
"City I think is the best team in the league," he added. "Arsenal are doing very well of course. But especially in home games, City is the team to beat."
Vertonghen will be in international action on Tuesday night when Belgium entertain Japan in a friendly in Brussels.
Among his Diables Rouges team-mates is striker Romelu Lukaku, on loan at Everton from Chelsea, who was involved in a collision with Hugo Lloris at Goodison earlier this month that caused concussion for the Spurs goalkeeper.
Vertonghen insists there was no deliberate intent from Lukaku in the incident and that the matter has now been forgotten.
"He's not like that," added the Belgium defender. "We spoke to him. I know he didn't mean to, he's a very kind guy.
"I hope everything's OK with Hugo now."