Mercedes non-executive chairman Niki Lauda sees Ferrari as his outright favourite to win in Singapore next weekend.
Mercedes' back to back wins at Spa and Monza have put Lewis Hamilton in command of the world championship fight.
After the German outfit inflicted a heavy loss on the Scuderia on its home turf, and even as the performance level of its W08 chassis continues to improve, Lauda still sees Ferrari prevailing around flood-lit Marina Bay street circuit.
"We won at Monza and that was a shame for Ferrari and their important event," the F1 legend told Italy's Corriere dello Sport.
"But in Singapore maybe Vettel will change things again.
"Many times Ferrari has been faster than Mercedes. At Spa Vettel was very close. Ok, at Monza perhaps a little less, but in my opinion this was due to a mistake in the Ferrari setup.
"Ferrari will be the favourite in Singapore, but on the other hand it is difficult to say who will win. I hope it is Hamilton."
The triple world champion and former Ferrari driver says that, despite the intense rivalry between the Silver Arrows and the Scuderia, he still has a soft spot for the red squad.
"My heart is with Ferrari but my head is with Mercedes. It's ok for me.
"Vettel is a number 1 driver," Lauda added.
"His heart is for Ferrari and if the team is competitive, you can't discount him."