Mercedes non-executive chairman Niki Lauda says Ferrari's resurgence this year has not been a surprise to him.
The Maranello squad had a torrid 2014 season, managing just two podium finishes on its way to a distant fourth place in the constructors' championship.
This season, however, Ferrari has emerged as Mercedes' closest challenger, and has finished on the podium in all races, including a victory in the Malaysian Grand Prix.
Lauda says that, given all the changes Ferrari underwent last year, it is only normal for the Italian squad to be back on form.
"I am not at all surprised by the improvement of Ferrari, because they started to work on it last season, they rely on the quality of work by (James) Allison, and because of the restructuring of the team," Lauda told Gazzetta dello Sport.
"The anomaly was last season, not this season. I never had the illusion that we would continue to dominate like that."
Lauda also said Mercedes will not react to Ferrari's engine allocation strategy.
Asked if Mercedes will now follow suit and give its contenders a fresh turbo V6 for Spain, he said: "No. We are only at the fourth race.
"What may seem a disadvantage now will become an opportunity when it really counts, in the second part of the season."