Sainz progress 'decisive', says Tost

The Spaniard missed out on promotion to the Red Bull team to Max Verstappen, but impressed with a series of strong drives, including sixth in Spain, USA and Brazil.

He outperformed team-mate Daniil Kvyat and scored over double the number of points he managed in his rookie campaign.

The Spaniard agreed a new deal to stay at Toro Rosso for 2017 with Red Bull, to which he is contracted, then had to turn down interest from Renault later in the year.

"I'm very impressed by his driving but I'm more impressed by his learning curve because this is decisive," Tost told Autosport.

"You can see that he's getting better and better but he's also committed to the positive attitude and we have a lot of fun working together with him.

"He has a very good technical understanding and gives really good feedback to the engineers.

"He also has a very good feeling in the wet as he saw in Interlagos and all these factors made him a very good driver."

Tost was impressed by the way Sainz dealt with missing out on the Red Bull drive and Renault's interest later in the year and believes he has plenty of time to move up the ladder.

"He's still very, very young and I think he knows that especially next year, Toro Rosso is the best team for him to run," he said. "I'm looking forward to next season.

"He's only 22 years old - in former days, drivers were not even in Formula 1 in this stage.

"The young drivers think that the time is running away but it's not running away.

"They are so young, there are still many possibilities.

"We will see with the new regulations where we end up."