Not if you do it right. Your pipe just needs to be much bigger than the outlet hole of the muffler.
I have my welder/generator in a similar situation. Basically an area next to my garage. A solid PVC fence encloses it on the side opposite to the garage, and the top is enclosed by an awning. One end is pretty open, the other is only partly open.
My solution was to use a 4" vent pipe that goes up 6' to a rain cap. It is attached to the end of the awning, with a contraption I made to insulated the wood from the heat of the stack, with a pair of elbows that keep the generator out of the rain.
That 4" stack points up. The generator points horizontal.
So, I used a 1 1/2" brass drain elbow that's 18" long. It is just a little bigger than the output of the muffler. It turns the exhaust up, and then extends 18", with just about all of the straight part going into the 4" pipe. I cut the brass in three slots at the end to keep it centered in the 4" pipe, punched a bunch of holes in it, and wrapped it in stainless pot scrubbers from the dollar store. A poor man's glass pack muffler, if you can picture it.
Now, the exhaust goes out over the roof, and the sound is much better too.
With the venturi effect, you can feel the open bottom of the 4" pipe sucking in cool air. Above where the brass ends, the pipe gets hot, but still nowhere near as hot as the muffler, as so much cool air gets mixed in.