Esteban Ocon replacing Pierre Gasly at Toro Rosso next season has been ruled out by Red Bull team principal Christian Horner due to his Mercedes links.

Frenchman Ocon, part of the Silver Arrows' driver development programme, is one of the most promising drivers on the grid but looks set to lose his seat at Racing Point Force India to Lance Stroll, whose father has purchased the team.

Renault snapping up Daniel Ricciardo ruled out one potential option for the 21-year-old, while McLaren deemed his Mercedes affiliation as "a tick in the wrong box" and opted for Lando Norris and Carlos Sainz Jr in their 2019 line-up.

And with Toro Rosso being powered by Honda, Horner says it is unlikely they will offer Ocon a seat unless he is released by Mercedes, which Toto Wolff this week suggested could happen to help him find a drive for next season.

"For what is relatively little investment by Mercedes it's been to their merit that they've helped these guys to get into F1," Horner told Motorsport.com.

"But now it seems to be almost an anchor being a Mercedes driver. Being on a recall mechanism isn't attractive to a vast majority of teams.

"The crazy situation is you've got a driver like Ocon who might end up without a seat next year. If he was to be contractually free he'd be an obvious candidate for Toro Rosso.

"But Red Bull aren't going to invest in a Mercedes driver, understandably. And I wouldn't expect the same to happen the other way around."

Mercedes have already extended the contracts of Lewis Hamilton and Valtteri Bottas, but Horner feels they may have benefited from putting faith in Ocon and pointed to Red Bull's success with promoting Sebastian Vettel, Max Verstappen and Ricciardo from Toro Rosso.

"It's very easy to go with something known and there's far more perceived risk in taking an unknown quantity or a junior, and I think we've demonstrated on numerous occasions that it pays off," he said.

"We've had a very successful junior programme, and Red Bull has a junior team, and has invested in that. It's paid dividends with Seb, Daniel and Max, and we'll see with Pierre Gasly [who replaces Ricciardo in 2019].

"And it's given numerous others opportunities, such as Carlos Sainz."