Red Bull Formula 1 chief Christian Horner says the team is waiting for the "right time" to open negotiations with Daniel Ricciardo over a new contract beyond the end of the 2018 season as it looks to secure the Australian's services in the long-term.

Red Bull announced over the United States Grand Prix weekend that Max Verstappen ensuring he would remain with the team up to the 2020 season, leading to questions about Ricciardo's future given his current deal expires at the end of next year.

Ricciardo has said he is not looking to rush into making a decision amid links to seats at Mercedes or Ferrari for 2019, but Horner stressed Red Bull will work hard to keep him when the time comes to open talks.

"He’s not going to conduct his negotiations through the media. At the right time we will sit down, but he knows where we are and that our intent is to keep him," Horner said.

"He enjoys being within the team, he sees the qualities and capabilities in the team and he knows how we go about our racing, how we treat the two drivers and he’s comfortable and happy with that.

"So I think he’s keen to see what engine performance looks like next year, which is understandable."

Horner said he understood why Ricciardo is looking to take his time before making a decision, and said he would not mind waiting six months to strike an agreement so long as it works in Red Bull's favour.

"We’re heading into year five of a five-year agreement with Daniel and he’s been with Red Bull for pretty much 10 years now," Horner said.

"I think as his character has developed and his personality has come across, he’s seen the fit between Daniel Ricciardo and Red Bull. I think he sees the capability that we have within the team and I think he’s very happy within the team.

"The next move that he makes at 28 years of age is a very important one for him, so of course he is going to take the time to make sure the decision is right for him.

"He knows the intention very clearly, and I’ve discussed it with him, is that we want him within the team.

"If that takes another six months then so be it."