Ralf Schumacher has described Max Verstappen's performance in final practice for the Miami Grand Prix as "frightening".
The Red Bull driver finished four-tenths faster than the rest of the field to send a message of intent ahead of qualifying, with Ferrari's Charles Leclerc his nearest challenger.
Two-time World Champion Verstappen is aiming to bounce back from a tumultuous weekend in Azerbaijan with pole position and the victory around the Hard Rock Stadium to stretch his advantage over teammate Sergio Perez, which stands at six points after the Mexican's victory last time out.
Speaking to Sky Sport DE post-FP3, former F1 race winner Schumacher said: "It is amazing, almost frightening how fast he [Verstappen] is. [Perez] is also in good shape."
"Verstappen is out of reach for everyone, [but] I would not underestimate Ferrari. Charles Leclerc has done well and they will definitely be there."
Mercedes struggled to only 10th and 13th in the final hour of running before qualifying with both George Russell and Lewis Hamilton complaining of issues.
The Silver Arrows were joined in the midfield by the Aston Martin duo and Schumacher has written off both team's chances of being competitive.
"Mercedes will be nowhere this weekend, they look a bit worse. The same is more or less true for Fernando Alonso as well."