Felipe Massa thinks Mercedes' mileage from the first winter test is an ominous warning to the rest of the F1 grid.
Mercedes completed 675 laps over four days in Barcelona, 200 more than nearest rival Toro Rosso. The world champions have dominated the V6 turbo era and Massa thinks its lap count this week suggests that could continue into 2016.
"Them doing so many laps is already a big warning for the season, along with what they did in the last two years and how they finished the season, and the car they have and with the same rules," Massa said. "It is a warning whatever the situation. What they're doing on the track definitely shows they're going to be very, very strong again."
Williams has had a mixed start to the winter, standing fourth on the mileage chart but having several delayed days. Thursday was one example, with an ERS issue limiting Massa to just 54 laps.
There are just eight days of testing this year due to the reduced winter schedule and Massa admits the team's problematic Thursday was far from ideal.
"It was not really a great day. We didn't do as many laps as we did [on Wednesday] and we had some issues that took time to change in the car.
"I think the only positive thing is that we did our aerodynamic tests in the morning to try to analyse all the numbers around the car. We've lost massive time and it was not a very useful day. I hope it won't disturb our understanding of the car."