Sebastian Vettel says it will still take time for Ferrari to catch Mercedes despite the Italian squad's impressive start to the 2015 Formula 1 season.
After a dismal 2014, Ferrari has emerged as Mercedes' closest challenger, with Vettel having won the Malaysian Grand Prix.
The German has been on the podium three times in four races, while teammate Kimi Raikkonen finished second last time out in Bahrain.
But although Ferrari has given Mercedes a run for its money so far, Vettel is aware that it will not be easy to close to gap to match the German squad's performance.
"We are trying to bother Mercedes, and we must be right behind them and pounce if something goes wrong with them," Vettel told Welt am Sonntag newspaper.
"But it is also important that we are not passed by other teams.
"Mercedes still have the strongest package. You don't make up such a deficit quickly.
"Ferrari have taken a step forward in the winter but it will take a while to be on the same level as Mercedes."
The Maranello team is expected to introduce a raft of aerodynamic upgrades at the Spanish Grand Prix this weekend.