Ferrari and Fiat president Marchionne famously set Ferrari the target of winning immediately in 2016, but all four races so far have been won by Rosberg.
"The drivers' title? I think we deserve it," the Italian, at the launch of the 2017 Alfa Romeo Giulia Quadrifoglio, is quoted as saying by La Repubblica. "Not because we are smarter, but simply as a reflection of the work we did in 2015.
"The most important thing now is to keep working. So far we have shown in at least three of the four races that we have the ability to be winners. Unfortunately due to mistakes, misfortune or other things, we did not succeed. But we have had four grands prix, and 17 remain. It's still open.
"Sochi was the most difficult for us. We needed an engine really at maximum power. If we had got out in front of Mercedes they would have had a hard time to pass us, especially if it had been Vettel at the front."
Ferrari's next chance to add to their tally will be the Spanish Grand Prix next weekend.