The pair tussled at Stowe, with Stroll passing Gasly for 11th off the track before they came together at Club later in the race.
The contact left Gasly with terminal suspension damage, while Stroll received a five-second penalty for causing the collision.
Asked by Autosport what had happened during the pair's battle, Gasly said: "To me it was quite clear and it's been always in the regulation he can't leave the track and gaining an advantage.
"On everything that I've seen he had four wheels off the track passing me, and that's gaining an advantage.
"I got down 15 seconds last weekend for track limits, now I lose a position today [because] someone getting off the track and nothing happens.
"Formula 2, Victor Martins was in the lead and got a five-second penalty for the exact same thing, so I'm just extremely confused with what's going on at the moment.
"And it just changes what follows after that... Get back behind him, I managed to get past him on the outside of Turn 7, after I managed to get past Carlos there, [he] passed us back.
"And then Lance takes us out of the race in the last chicane. So just extremely disappointed because the first part of the race was going well.
"We were chasing Fernando, there was good speed. I just lacked some straightline speed to try something and get a move on him, but it was still good to be in that pack, and then all our efforts get ruined with what followed. So disappointed."
Source: Autosport