Hartley, 27, said it was an unbelievable feeling to be contemplating a debut at last and felt ready for it at a track he already knows from world endurance.
"What an incredible feeling!" said Hartley, who won the Le Mans 24 Hours this season and was world sportscar champion in 2015.
Toro Rosso team Principal Franz Tost reportedly wants to use next the race as a chance to evaluate a new driver to add to next year's roster and while Gasly remains a favourite to retain one of the team's cars, the other is now up in the air.
But there were actually two open seats at Toro Rosso for next weekend's race since Pierre Gasly has prior commitments in the Japanese Super Formula series.
Discussing Hartley, New Zealand racing legend Kenny Smith - who is also his mentor - said: "Brendon didn't like anybody ahead of him". In the June of this year he won the prestigious Le Mans 24 Hours with Earl Bamber and Bernhard.
The shake-up was required because Spaniard Carlos Sainz has moved to Renault for the final four races of this season in preparation for a full year with the French team on loan from Red Bull in 2018. 'This opportunity came as somewhat of a surprise, but I never did give up on my ambition and childhood dream to reach F1.
Trump, Trudeau differ on NAFTA talks
Today, Prime Minister Trudeau arrives in Mexico for meetings with President Enrique Pena Nieto. Chamber of Commerce has labeled "poison pill proposals" that threaten to torpedo the talks.
"COTA is a track I really enjoy and one I have raced at recently".
Coming off a win last weekend at IMSA's Petit Le Mans season finale in a Tequila Patron ESM Nissan DPi, Hartley has become an incredibly popular solution as a stand-in solution between FIA WEC obligations with Porsche.
He tested for Toro Rosso at the end of 2009 but has not driven an F1 vehicle since a one-day test for Mercedes in 2012.
The 2017 Le Mans victor has emerged as a front-runner to gain the US Grand Prix audition after years as a reserve driver and time in the junior programme with the Red Bull team.
"I've got a lot to learn in one week but I feel ready for it, honestly".
Should he compete in the race he will become New Zealand's first F1 driver since Mike Thackwell in 1984.
"I'm convinced he'll do a fantastic job for us".