Six races into 2019, the driver 'silly season' looks set to kick off.

The most explosive rumour is that four time world champion Sebastian Vettel, under huge pressure at Ferrari this year, could be contemplating retirement at the end of the season.

In Monaco, he admitted his role in Ferrari's issues.

"Well, I'm part of the team so I don't put myself above," said the 31-year-old German.

"I've had some difficult moments this year where I'm fighting the car, but I think it's linked to the fact that we struggle to put our car in the right window."

If he does retire, the seat alongside Charles Leclerc would presumably be filled by a driver like Valtteri Bottas, Nico Hulkenberg, Kevin Magnussen or Sergio Perez.

But Fernando Alonso is also being linked with it, especially as Ferrari's management has changed since he fell out with the Italian team in 2014.

Interestingly, there are also rumours that Hulkenberg - who currently drives for struggling Renault - opened talks with Red Bull in Monaco.

It has been said he might replace Pierre Gasly, but another rumour is that if a seat at Mercedes opens up - for instance, if Lewis Hamilton retires - Max Verstappen could head to the silver team.

"In 2014, the rift between Ferrari and Fernando Alonso had a domino effect on Red Bull, who then lost Vettel," an unnamed team source told Sky Italia.

"Let's say Hamilton or Sebastian decide to stop, which is admittedly unlikely, then teams like Ferrari or Mercedes must have a plan B at the ready.

"So we've heard rumours of something existing between Verstappen and Mercedes, as well as between Daniel Ricciardo and Ferrari.

"And what happens if Red Bull finds itself without Verstappen? In Monaco, I understand that they checked in with Nico Hulkenberg," the source added.