Toro Rosso team principal Franz Tost has said that Daniil Kvyat's "mistakes of his own making" have contributed to him being dropped from the team.
Kvyat has secured just four World Championship points this season and has seen the 'Torpedo' nickname return due to a number of incidents that has put him on the verge of a one-race ban.
While Tost concedes that the Russian has not been helped by technical issues, the Toro Rosso boss believes Kvyat has had made a significant contribution to his own downfall.
"For a variety of reasons, some of them due to technical problems, but others being mistakes of his own making, Daniil Kvyat has not really shown his true potential so far this year, which is why we are standing him down for the next races,” Tost said.
"This will give us the opportunity to evaluate Pierre on track during a proper race weekend."
Tost continued by saying that Gasly has earned his chance to impress and the change will ultimately help the team settle on their 2018 line-up.
"Scuderia Toro Rosso was established by Red Bull to bring youngsters from its Junior Programme into Formula 1 and that's what we are doing by giving Pierre this chance.
"He is the next in line at Red Bull for this opportunity and he has shown that he deserves it, having taken the 2016 GP2 title and this year being very competitive in the Super Formula series in Japan.
"He really has a valid chance of winning the title, as he is only half a point behind the leader. The driver switch gives us an opportunity to make a more informed decision regarding our 2018 driver choices."
Gasly was due to replace the Renault-bound Carlos Sainz but, with Jolyon Palmer playing hardball in negotiations over an early exit, it has left Toro Rosso turning to Plan B in order to get Gasly onto the grid.