Ralf Schumacher believes Red Bull have the advantage to start the 2021 season, with Mercedes on the back foot due to an unstable rear end.
While Red Bull set the pace overall at the pre-season test, with Max Verstappen's best lap more than a second clear of the best Mercedes' time, Schumacher thinks Mercedes are being affected by aerodynamic changes that have affected stability.
"Mercedes seems to have problems with the car. The rear end seemed very unstable. That's why Red Bull is ahead for me at the moment.
"But it's also clear that Mercedes hasn't shown everything yet and drove with more fuel on board. They have to get the problems under control as quickly as possible now, otherwise it will be close compared with Red Bull."
Elaborating on where he feels the problems with the W12 lie, Schumacher said: "It looks as if the rear wing, which is extremely important for a stable rear, is not always optimally hit by the airflow. So we're talking about an aerodynamics problem. From my experience I know that something like this is not very easy to solve."
Referring to that experience from his time as a Formula 1 driver, Schumacher said Williams introduced parts in 2003 that simply didn't work.
"McLaren, the team that had to be beaten alongside Ferrari at the time, brought in new deflectors that Williams wanted to copy.
"Somehow it didn't work as we wanted, the car was unstable and difficult to drive.
"In the first race in Australia I came into contact with another car and lost one of the wind deflectors. Then the car was suddenly much better and drove three tenths of a second faster per lap!
"After that, the parts on the car were no longer seen. That just goes to show that small parts can often have a big impact."