A straight sets doubles match shouldn't be that difficult on the body, I don't see why is that a problem, unless he already had problems after the first match?
Laurendeau is an idiot. Raonic had some knee issues while training in Toronto even before going into the first match. Save him for the 2 singles matches.
Instead, let's take a guy with some knee trouble, put him in doubles where he's not familiar, and make his knee start and stop a whole bunch for 2+ hours.