Double F1 world champion Mika Hakkinen says Lewis Hamilton will only remain in the sport as long as he has the drive to win.
Hamilton won the title for the fourth time in 2017 after a brilliant second half of the season with the Mercedes team and is contracted to the German outfit until 2019.
However, the 32-year-old has openly spoken about his potential retirements plans.
But Hakkinen says Hamilton will stay in the sport as long as he has the desire to add to his CV.
"Lewis' achievement in winning four world championship titles is impressive, and you can see that he has kept the hunger alive, that is critical," Hakkinen wrote on his Unibet blog.
"When I won both my world championships in 1998 and 1999, I went into 2000 absolutely determined to win a third title, but it was not to be.
"After that year, when I felt my energy levels drop a little, it was not long before I retired."