The driver 'silly season' is really shifting into high gear in the paddock in Austria.

The big news is that a performance or results clause in Max Verstappen's Red Bull contract is in play, amid rumours he is eyeing a switch to Mercedes.

"I confirm that there is a performance clause, but we make no further statement," the Dutchman's manager Raymond Vermeulen told the Dutch publication Formule 1.

"Red Bull knows exactly what the agreements entail."

It is believed the clause is in effect until the summer break, and says that unless Verstappen is in the top three points positions by then, he is free to leave.

Dr Helmut Marko, the Red Bull driver manager, also confirmed the existence of the clause. It is rumoured it might also stipulate a race win for Verstappen by the summer break in order to secure his services for 2020.

Verstappen, 21, says he is happy at Red Bull but doesn't want to wait until he is "35 or 40" before retiring as a world champion.

Manager Vermeulen said: "We want to become world champion with Red Bull. We feel very comfortable but we want to win.

"We started with them in 2015 with the plan to become the youngest champion ever.

"We are not only concerned about next year, but also the years after that. What will happen to Red Bull and what will happen to Honda? All the elements are important," Vermeulen added.

Marko is clearly now putting pressure on Honda to provide a more powerful engine for Verstappen.

"What we lack is power," he told Krone newspaper in Austria. "Honda is in the process of fixing that.

"Our next development should come in Spa and Monza, then we should be closer to Mercedes. But it takes time."

If Verstappen does leave Red Bull, the equally sensational rumour is that Sebastian Vettel could replace him.

"Seb has often been seen with his old friends at Red Bull lately," a source said.

And Corriere dello Sport claims that if Vettel leaves Ferrari, the Maranello team could reunite with Fernando Alonso.