New Zealander Evans has been ruled out by a foot injury suffered during the victory over Aviva Premiership title rivals Saracens at Wembley last weekend.
Rory Clegg will wear the number 10 shirt at Stade Felix Mayol, replacing Evans, whose last-gasp conversion gave Quins a thrilling win against Stade Francais in the Amlin final almost a year ago.
England skipper Robshaw, meanwhile, aggravated a knock during the team run, so Luke Wallace deputises alongside back-row colleagues Tom Guest and Nick Easter, with lock George Robson leading the team.
Quins rugby director Conor O'Shea highlighted discipline as a key factor for his players ahead of the Toulon clash, admitting "some very dumb penalties" were conceded against Saracens.
And England international full-back Mike Brown knows that area must be watertight, especially as points machine Jonny Wilkinson will start for Toulon.
"Discipline has been talked about," Brown said. "It is something we have to improve if we want to go well in the Amlin and stay where we are in the Premiership.
"It's especially true with Wilko this week; that will be a massive test of our discipline.
"It was a tough game last week, but we always we knew it would be. Saracens aren't the champions of England for no reason.
"They threw everything at us and we managed to hold out, but there is plenty to work on. Our discipline could have let us down."
Toulon will field a galaxy of international stars against Quins, including Wilkinson, centre Matt Giteau, prop Carl Hayman and number eight Joe van Niekerk.
But Quins can reflect on a Heineken Cup away win over European heavyweights Toulouse this season - they subsequently went into the Amlin as a group runner-up - which should give them confidence.
"We won at Munster last year, we did well at Toulouse and we did well at Gloucester this season, which is another hard place to play," Brown added.
"We will take confidence from those performances, but this is a completely different game.
"I have never experienced Toulon before, and I don't think this club has either.
"I've heard their war-cry on the television, but I haven't experienced it first hand. They've got a brilliant atmosphere at their ground and the French fans are usually really passionate. I think any rugby player would enjoy playing over there.
"It's a big challenge as they've got some world-class players.
"That is why this competition is so good now. Toulon are a brilliant team and this could easily be a top-tier Heineken Cup game.
"We are massively looking forward to it. How can you not? These are the type of teams and these are the type of players you want to play against."
Victory for Quins would see them play a home semi-final against Stade Francais or Exeter on April 27, with Wasps or Biarritz hosting Brive or Scarlets in the other last-four encounter.
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