That bonus-point success at Adams Park saw Wasps set up a last eight tie with their English rivals in High Wycombe on the weekend of April 3/4/5/6 but Varndell won't feature as he faces 12 weeks on the sidelines.
It is the second time this season that the former Leicester Tigers and England wing has suffered the same injury, with the first setback coming in the opening game of the domestic season and costing him three months of action.
Varndell missed the first three rounds of the Amlin Challenge Cup but has made a huge impression since his return, scoring a try apiece in the wins over Grenoble and Bayonne before bagging a brace against the Italians at the weekend.
He was joint top scorer in the Aviva Premiership last season - alongside fellow Wasps wing Christian Wade - and had recently been recalled to the England set up after a lengthy absence. Varndell was due to play for England Saxons against the Irish Wolfhounds on Saturday but he will now have to wait until at least the summer for a chance to reignite his international career.
The news is a big blow for Wasps, especially given that Wade is already unavailable with a foot ligament injury that will see him miss the remainder of the season. Centre Ben Jacobs and scrum-half Jack Moates were also recently ruled out until at least the summer, while full back Hugo Southwell is still struggling with a hamstring problem that shows little sign of progression.
There was some good news for Wasps at least today, though, with Italian veteran Andrea Masi returning to full training and Wade putting pen to paper on a new deal. Masi will play some part in Wasps' LV= Cup fixture this weekend, while Wade has turned down advances from elsewhere to remain with Dai Young's side for 'the foreseeable future'.
"Christian is, without doubt, one of the outstanding young talents in the country at this moment in time. He is a young guy with a level head on his shoulders who is always keen to learn and I think that has been obvious in his rapid development in the last few seasons," said director of rugby Young.
"We have got a really good core of young, talented, English players who will form the backbone for this squad moving forward and I am hugely pleased to add Christian's name to that list."
"The last few years have been amazing for me," added Wade. "Playing for England is a dream come true and pulling on a Lions jersey in the summer was something that I never expected. It was Wasps who gave me the platform to go on and do those things and I am extremely grateful for the opportunities they have provided me.
"Since I first made my debut for the Club, things have changed dramatically and we are now building towards something that we all believe in and want to be part of. I'm excited about what the next few years will bring and am delighted to be here for the foreseeable future."