Formula 2 championship leader Lando Norris has been approached by Toro Rosso to take over Brendon Hartley's position at the team for the rest of the season.
Norris is the reserve driver for McLaren this year, but Toro Rosso made a formal move to sign the 18-year-old on loan as a replacement for Hartley. Press Association Sport reports Toro Rosso wanted Norris to make his debut in Austria next month -- just seven days before his home race at Silverstone -- but the move was blocked by McLaren.
It is believed Toro Rosso, the team with which Sebastian Vettel and more recently Max Verstappen spent their formative years in the sport, were keen for the temporary deal to be extended into next season. But McLaren's plans beyond this year remain undetermined, and the British team could yet choose to promote Norris to one of their race seats in 2019.
Fernando Alonso, 36, may turn his back on F1 at the end of the year, while there are also doubts as to whether Stoffel Vandoorne will be retained. McLaren may also have feared risking losing their protege on a permanent basis to rivals at Red Bull.
A McLaren spokesperson told Press Association Sport on Wednesday: "We are not surprised that other teams approach our drivers. They clearly believe they are as talented as we do."
Norris, from Glastonbury in Somerset, has already been earmarked as the next Lewis Hamilton after he won last year's Formula 3 series before landing the reserve seat at Hamilton's former team McLaren. The teenager holds a 27-point lead in this season's Formula 2 championship, the feeder series to F1, and won impressively on his debut in Bahrain in April.
Hartley has come under increasing pressure at Toro Rosso this year after a series of lacklustre performances. He has scored just one of Toro Rosso's 19 points this season, and an accident in final practice at the Spanish Grand Prix cast fresh doubts over his future of the team.
Red Bull's driver programme is known for being ruthless and Hartley was drafted back into the fold last year after Daniil Kvyat was dropped by Toro Rosso. Historically Red Bull has supported young drivers from karting to F1, but with its latest protege Verstappen it plucked him from F3 and dropped him straight into an F1 drive.