Vincent Janssen has struggled since £17m Tottenham move
Janssen joined Tottenham last summer for £17million after a stunning campaign at Dutch side AZ Alkmaar.
The 22-year-old striker scored 27 goals in 34 Eredivisie appearances but has failed to carry over his form into the Premier League.
He's found the back of the net just five times in 33 games across all competitions, with four of those coming from the penalty spot.
Vincent Janssen helped Tottenham to 3-1 comeback win over Swansea
But Vertonghen, who joined Spurs from Ajax in 2012, has backed Janssen to kickstart his White Hart Lane career after playing a vital role in Wednesday's 3-1 win at Swansea.
The 29-year-old defender told the Evening Standard: "You get a lot more space [In Holland]. Every team in Holland wants to attack and they don't really think about defending.
"That's the philosophy – just play 4-3-3 and play good football in possession, and don't think too much about defending.
"That's why I think strikers get so many chances and goals in Holland, and obviously it's different here.
Jan Vertonghen backs Vincent Janssen to succeed at Tottenham
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"I think the tactics are less naïve. Swansea defended for 90 minutes but they were very close to beating us.
"But Vincent is adapting very well now. He understands the way the gaffer wants him to play. He's so strong, he just needs that goal and then he'll be on fire.
"I'm so happy for him. Vincent's working very hard. Obviously it wasn't the start he wanted but he's showing now what he's capable of.
"He made a big difference when he came on against Swansea. Can he succeed in the Premier League? Definitely, yes. I am convinced of it."