Daniil Kvyat says he has changed his approach to formula one since being dumped at the end of 2017.
Marko says Kvyat is obviously stronger and calmer for his Toro Rosso return.
"Time will tell," Kvyat told El Mundo Deportivo.
"The only thing I can say is that I have changed some things in my way of preparing for races and my work. And I strongly hope that it will lead to an improvement in my driving."
Asked what changes they are, he answered: "I don't want to say. I don't want to reveal anything. I want to make it clear on the track."
Last year, Kvyat spent the year working with Ferrari in the Maranello team's state-of-the-art simulator.
"I think it was a very, very positive year," said the Russian.
"It was good to work in a slightly different environment like Ferrari. They were very good to me and at a certain point I was so hungry to return to F1.
"It seemed to me to be very difficult to go back, but then the opportunity came.
"There were a few negative days but only a few, because it was a very positive year. Everything cannot always be easy. Sometimes it is good to live some ups and downs and that year helped me to have more hunger," said Kvyat.
But the pressure is on, especially as Marko has declared publicly that 2019 is Kvyat's "last chance".
"F1 is like that," Kvyat insisted. "You always have to do well.
"Maybe if you are a world champion you can have a bad period, but when you are in the middle zone, you always have to be at your best level. You can't have 3 or 4 'off' races."
But he is positive that 2019 will be a good year for him.
"I have a great team around me who helped me to digest the past and understand what I had to improve as a person and a driver," said Kvyat.