Toro Rosso team principal and Max Verstappen’s former boss, Franz Tost, believes the presence and improvement of the Dutchman at Red Bull was ultimately the reason why Daniel Ricciardo opted to leave the team in favour of Renault last year.
Verstappen is viewed as one of the most talented drivers on the grid and a future world champion, with Red Bull reportedly considering him as their main driver on the grid ahead of Ricciardo.
Tost reckons Verstappen was so impressive that Ricciardo thought he could have better luck elsewhere.
"Max is currently one of the fastest drivers,” the Toro Rosso boss told Motorsport.com.
“I think one reason why Ricciardo left was certainly Max. Because he thought to himself: 'I won't beat him so easily anymore’."
The Austrian believes Verstappen is getting better and better, and part of the reason for that is his increased maturity on the track, compared to his aggressive nature in recent years.
“He realised that he doesn't always have to go through the wall with his head,” Tost said.
“Now he's reached a level where he'll compete for victories and the world championship if everything comes together.
"He also showed super overtaking manoeuvres where you didn't get the impression that it was on a knife's edge. He really has this maturity now that makes it possible for a driver to compete for a world championship.”
The 21-year-old is currently third in the driver’s championship for 2019.