Sebastian Vettel is to leave Ferrari at the end of the year after contract talks between the two broke down with no agreement.
The move, which is expected to be officially announced imminently, throws the future of the 32-year-old four-time world champion into doubt.
Spaniard Carlos Sainz, currently a McLaren driver, is among those who have been linked to Vettel's seat.
If Sainz leaves McLaren, one option for the team is Renault's Daniel Ricciardo.
The Australian had serious talks with McLaren in 2018 when he was weighing up whether to leave Red Bull, before finally deciding to move to Renault.
Ricciardo is known to be unsettled at the French team and has talked about moving on.
Vettel could also be an option for McLaren, if he felt he was prepared to move to a team that was going through a restructuring process.
If not, the options for the 32-year-old to continue in F1 are bleak.
Lewis Hamilton, who is also out of contract at the end of the season, has repeatedly signalled his intention to stay at Mercedes, who are not believed to be considering a move for Vettel.
And Red Bull, where Vettel won his four world titles, have said that they would not partner their star driver Max Verstappen with another top-line driver - nor is Vettel likely to be interested in partnering the Dutchman.
Ferrari's other options are Ricciardo or Italian Antonio Giovinazzi, who races for the affiliated Alfa Romeo team.
Hamilton is not considered to be a serious possibility.