Helmut Marko has refused to rule out a move to Honda power for Red Bull at the end of the 2018 Formula One season, saying "everything is open".
Honda have endured a difficult time since returning to the sport with McLaren in 2015, managing two ninth-place finishes either side of ending the season sixth in the constructors' standings in 2016.
McLaren have partnered with Renault for the 2018 campaign, as Honda enter a new arrangement with Toro Rosso - Red Bull's sister team, who are also overseen by Marko.
In an interview on the F1 website, Marko was asked whether a successful partnership between Toro Rosso and Honda could lead to a future deal between the Japanese engine supplier and Red Bull.
"We are very happy with the Toro Rosso and Honda cooperation," he said. "Toro Rosso will put all its efforts into making a competitive chassis.
"We do believe in Honda - otherwise we wouldn't have made that deal. I am very impressed with the facilities that they have - and their determination to win.
"It is just a matter of bringing everything together and we believe that this moment will arrive sooner than everybody is expecting.
"We will observe very closely - beyond 2018, everything is open!"
Red Bull could be left with no option but to switch to Honda power for 2019 should they not extend their deal with Renault.
Ferrari and Mercedes are understood to have little appetite to add to their current supply commitments, leaving Honda as the only other manufacturer on the grid.
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