Dr Helmut Marko admits he was "very worried" that Max Verstappen could quit Red Bull and switch to Mercedes for 2021.
It was announced on Tuesday that the Dutch driver is staying at Red Bull until at least the end of 2023.
"I spent the holidays fixing the contract," Marko told Auto Bild. "I was very worried about losing Max to Mercedes in 2021."
It is believed 22-year-old Verstappen's salary has been doubled or tripled, and that part of the new deal is that Red Bull guarantees him a top engine.
"We currently have that with Honda," Marko said. "I am also optimistic that they will continue," he added, referring to the fact that Honda for now is only committing to F1 for 2021.
As for that tripled salary, Marko admitted: "The new contract was not cheap. But I didn't feel like playing poker."
Indeed, while Ferrari has tied down Charles Leclerc for the long term, Verstappen has openly flirted with the possibility of switching to Mercedes.
"This is a very important step for us," Marko told Auto Motor und Sport. "Now we can look to the future with more confidence."
The 76-year-old Austrian said he was spooked by recent rumours linking Lewis Hamilton with Ferrari, which would have opened up the key seat at Mercedes.
"To be honest, we had a hard time guessing what was going on with the Ferrari and Hamilton story," said Marko.
