Brendon Hartley has emerged as the leading contender to replace Pierre Gasly at Toro Rosso for next week's US Grand Prix in Austin.
With Carlos Sainz moving to Renault and Gasly returning to Japan to compete for the title in the final round of the Super Formula series, the Faenza-based outfit is bringing back Dany Kvyat but still has a seat on offer for Austin.
Team boss Franz Tost is keen to evaluate a driver for 2018 and Kiwi Brendon Harltley is apparently a favourite to fill the interim seat.
The 27-year-old and Porsche factory driver is no stranger to F1, having been Red Bull's reserve driver in 2009 and 2010 before he was dropped from the company's driver development program.
Hartley also ran with Mercedes in a young driver test at Magny Cours in 2012.
It could be a busy two weeks for Hartley as he'll be racing with Porsche at Fuji in the World Endurance Championship, and competing for the category's title.
Negotiations are likely underway between all relevant parties to smooth out contractual issues to enable Hartley to compete with Toro Rosso in Austin.
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