Quins currently occupy ninth place in the Aviva Premiership, having won just seven of their 15 games this season.
Conor O’Shea’s side are used to competing for a play-off spot, having finished in the top four in each of the past three seasons.
They were champions in 2012, but have not managed to scale those heights since and are currently 10 points adrift of fourth-placed Exeter and third-placed Saracens.
But Saints forwards coach West said: “They’re a side with a lot of quality. They play a lot of rugby and they push you around the pitch.
“You’ve got to make sure your defence is fully switched on and ready for what they’re going to throw at you because they could go from anywhere.
“They a play a really exciting brand of rugby and we know we’re going to have to be as good defensively as we were when we beat them at Twickenham to make sure we limit their chances.”
So is West surprised to see Quins, who Saints beat 30-25 in December, sitting ninth?
“I’m not really surprised because if you look at the points difference between third and ninth it’s very tight,” he said.
“There’s lots of things that are going to change over the next few weeks and there are a lot of good sides in the league - it’s a tough environment.
“It’s very competitive and though I’m not surprised where are Harlequins are at the minute, I wouldn’t be surprised if they strung some results together and pushed themselves into contention.
“Quins are in a position they’re not used to being in at this time of the year and that makes them even more dangerous because they’ll be fighting to right that situation.”