Damon Hill believes Lewis Hamilton will face a stern challenge from within Mercedes this season as Nico Rosberg's second defeat has made him "more determined."
Last season Rosberg lost the title to his team-mate as Hamilton pushed him wide on the opening lap of the United States GP before charging to the victory that he needed to wrap his third title.
Rosberg was angered by the situation, evident in the bit of cap tossing that went on after the grand prix. The German bounced back to win the final three races of the season.
Hill reckons Rosberg will have learned from last year's championship defeat and will be even more determined to get one back against Hamilton this season.
"I think he is a little bit more formidable," the 1996 World Champion told Sky Sports.
"I think after the Austin defeat, the day when he lost the championship and Lewis infamously tossed the cap and he tossed it straight back, I think there was a moment where Nico said 'okay, I am not going to take this anymore' and he did go ahead and win all the remaining races.
"He can go on ahead and become the other world champion's son to become a World Champion himself. He probably knows time is running out and when you get all those ingredients together you maybe get a little bit of a hardening of the determination. Maybe he will be more determined this year and harder to beat."