Germany's Bild newspaper claims that the championship leader's campaign will get a 15 horse power boost.
However, Vettel insisted: "I don't know if it will make a big difference."
"It was a planned change but it shouldn't change the hierarchy," he is also quoted as saying by Italy's Mediaset.
Vettel's teammate Kimi Raikkonen added: "We should be strong here, but it's not a matter of the engine - it's the overall package that makes the difference."
Ferrari will be looking to close the 33-point gap to leaders Mercedes on Sunday.