Jenson Button has conceded that Mercedes will be genuine title contenders following Nico Rosberg's maiden grand prix victory in China last week.
The German led from start to finish as Mercedes secured their first win since re-entering the sport three years ago.
That performance has led Button to confess that the Brackley-based outfit, for whom he won a world championship while they were under the ownership of Brawn GP, will rival his McLaren team and Red Bull for this year's constructors title.
"I spent a lot of years with that team - most of my career was with that team - so I am very happy for them they've achieved a grand prix victory this year," Button told the Press Association.
"There's a great bunch of people there, and people that went back to the team as well that I used to work with, like Geoff Willis, so that does obviously pose a threat to us in the championship."
Meanwhile, security concerns continue to hover over this weekend's race in Bahrain after four Force India team members were caught in a petrol bomb attack.
