Harlequins director of rugby Conor O'Shea says his side's Premiership season hinges on Saturday's clash with league leaders Saracens at Wembley.
Sixth-placed Quins are five points adrift of the play-off places, with three games of the regular season remaining.
"If we are going to be in the top four, we have to win this weekend, full stop," O'Shea told BBC Radio 5 live.
"This is do or die for us in the league."
Opponents Saracens won the Premiership last season and look certainties for a home-semi final, having also reached the latter stages of the European Rugby Champions Cup.
"The game against Saracens is won or lost in one way - and that's a physical battle," O'Shea continued.
"You have to be up for the physical battle and be prepared to go to war. It's as simple as that."
Last year's corresponding fixture attracted a world-record club crowd of over 84,000, with a similar attendance expected this year.
"Everyone wants to play this weekend," O'Shea said. "They just want to be around games like this."
After joining Harlequins in 2009 and guiding them to the European Challenge Cup in 2011 and the Premiership title in 2012, he will leave The Stoop at the end of this season to become the head coach of Italy's national team.
"I'm really excited by that but I'll think about it when it comes," the 45-year-old said.
"I just hope this group of players fulfil [their potential]. I've said to [captain] Danny [Care] many times this year that I just want to see him lift some silverware."
And the Irishman hopes his impending departure will not be a factor in how Quins finish the season, with the club in the semi-finals of the Challenge Cup as well as in Premiership contention.
"I love the place, it's been six years of my life," he added.
"But the game is never about coaches. The day the coaches believe it's about them, it's a sad day. This is about players, and it's the players who sacrifice so much.
"I've grown to admire some of these fellas so much. That I will miss, because they are very, very special people.
"Hopefully I've earned their respect, because they've certainly earned mine."