"It is going to be an incredibly tough game for us," said the former British & Irish Lions captain. "From all the other seven sides in the quarter-finals they are probably very happy they have got us at home.
"They are full of confidence; they are the Premiership champions; they have lots of English internationals - along with Nick Evans at No 10 - and came through their group relatively unscathed.
"They can play either an expansive or a tight game and we will be massive underdogs. To win these big games you need to perform really well but we have been here before."
The clubs met in the 2011 Amlin Challenge Cup semi-finals at Thomond Park with Harlequins winning 20-12 en route to lifting the trophy.
That was international scrum half Conor Murray's first European home game - and the scars are still raw.
"That was a hard day," he said. "It was my first European involvement after we beat Brive in the quarter-final over there. It was my first European home game with Munster and it was an unbelievable day, a sunny, dry day, a packed house, and just an unbelievably sad day.
"It was just a hard one to take because there was such a buzz around the city at the time and everyone was nearly expecting us to win, and we didn't. It was just a shock to the system."
"We're not unaware of people writing us off and we've probably had that underdog tag that you link with Munster down through the years.
"So that's definitely going to be an extra motivational tool this week and it's probably been talked about during training and at meetings before training, that there's people writing us off.
"There's a lot of confidence in the squad, in terms of us playing quite well during the year at times. We haven't been consistent but we have shown we have the ability to play quite well so we're going to try to draw that out.
"This is a huge game. It could be a great day so you've got to gee yourself up and get energised about it in training, and try to gee up some of the lads who might be feeling the defeat still, get them excited about what could potentially happen at the weekend."