Briton Jenson Button on Thursday conceded that his McLaren team will face a tough battle with Mercedes in this year's world championship after the Germans proved their potential with Nico Rosberg's win in China last Sunday.
Speaking ahead of this weekend's controversial Bahrain Grand Prix at Sakhir, the 2009 drivers world champion confirmed that Rosberg's commanding lights-to-flag triumph, following the FIA's rejection of all protests about their car, signalled that they are likely to be among the main contenders.
The victory was the first secured by Mercedes since they re-entered the sport three years ago, buying out the Brawn outfit that had just carried Button to the title.
Many of the team remain at their Brackley base and Button, who knows them well, has no doubt that they are capable of turning their performances into a championship bid.
"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," he told reporters.
"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."
After shining in the cool conditions in Shanghai, Mercedes face a different challenge with Bahrain's searing heat this weekend and it is likely to dilute their competitiveness.
But Button believes they will remain close to the front.
"They'll be quick," he said.
"In qualifying, they are phenomenal and they have been all year. The first time Nico got it together in qualifying was in China, so they are going to be competitive, and it's great to see that they are. As I say, I'm happy for them, but that's done now and we're fighting."
Button himself believes his and McLaren team-mate, 2008 champion and fellow-Briton Lewis Hamilton's performance this weekend will depend on their tyres' performance and tyre management.
The team's MP4-27 car has performed better in warmer weather this year and is therefore considered among the favourites at the hot desert-bound Sakhir circuit.
But Button warned: "The tyres are so important - understanding them, making them work, getting them into the sweet spot, either by skill or good fortune, or vice versa - it really matters.
"If you fall outside the sweet spot, by lack of skill and lack of fortune, I think you can really find it very difficult.
"I think we're competitive and I think the important thing is we've got two great racing drivers and I think we can qualify better than we did (in China) and I think we can race well.
"This is a season where we've had three very different races, we're going to have potentially 20 very different races this year and I think that's fascinating really.
"In a sense, I enjoy it and I'm sure people watching it really enjoy it. Who's going to predict who's going to win? I don't know!
"I've got no idea whatsoever. I'd like to think it's us but I think we'll have to see when we get there."
Mercedes' win in China, their first as a works team since the 1955 Italian Grand Prix, came at the end of a week that saw a protest against their controversial 'double' Drag Reduction System (DRS) rejected by the ruling body, the International Motoring Federation (FIA).