Ferrari's pre-season pace has caused concern within Red Bull, especially after their sandbagging tactics in the second week of testing, admits Helmut Marko.
The Italian team offered glimpses of their potential during the two weeks in Barcelona as they set the standard on a number of occasions.
Four-time world champion Sebastian Vettel twice set the fastest time of testing, even though there were claims Ferrari had lifted off to avoid showing their full speed.
And Marko believes Vettel and team-mate Kimi Raikkonen are serious title contenders if they still have more to offer when the season begins in Australia this month.
"Ferrari is very strong and reliable as well," Marko told Red Bull's Servus TV channel. "That's the difference to last year.
"What worries me somewhat is I know Vettel very well. He provocatively lifted on his fastest lap on the start and finish straight. Everybody could tell.
"And if you do something like this, then your self-confidence and the knowledge about having a lot more in the car is huge.
"Nobody has shown his cards properly. If you carry 10 kilograms more fuel, you gain about 0.35 seconds.
"Furthermore, engine mappings differ. This can gain you up to one second - or it doesn't.
"A lot has been kept in the dark. But if the race [in Melbourne] would have taken place with the same kind of temperatures we had [in testing] then Ferrari would be in front, for sure."