Felipe Massa says Lewis Hamilton cannot let his focus slip this season as Nico Rosberg tries to take the crown from his Mercedes team-mate.
The duo have been the title protagonists the past two seasons, however, both years went to Hamilton as he added to the title he won in 2008 with McLaren.
But in the closing stages of last year's championship it was Rosberg who came to the fore as the German won the last three grands prix.
It was, some claim, a sign that Hamilton had switched off have wrapped up the title.
Massa, though, reckons he cannot afford to do that at all this year as Rosberg will be making life very difficult for his team-mate.
"We saw Nico win the last three races, so it shows that maybe Hamilton was a little less interested in the last three races compared to how he was before because he was doing an amazing championship before," the Williams driver told Sky Sports.
"I think Lewis needs to be a bit more focused now as I don't think he is going to have a very easy championship inside his team looking at what Nico did in the last races. He will need to be very focused."