Having spent his Formula 1 career so far with tail-ender HRT and midfield contender Toro Rosso, Ricciardo will have his first proper shot at grand prix wins when he replaces Mark Webber in the second Red Bull next year.
Asked if he felt Ricciardo was ready for the Red Bull promotion, Vettel replied: "It is difficult to say because at the moment he is not in a car that allows him to score points regularly and race in the area where we race.
"People probably have the opinion that drivers that are in an average car or in the midfield are not on the same level as the drivers at the front.
"I think on average that is probably the case, but how do you get to step up if you never get the chance? It's a great time for him.
"Looking back, I was very lucky I got the chance to prove myself.
"I'm very sure Daniel is pushing very hard. Next year he will be trying to do everything to beat me.
"I'll have another Australian trying to make my life difficult..."
The champion declined to comment on whether he expected easier relations with Ricciardo than he has had with Webber.
"We are not best friends, yes there's reason to know that," Vettel said of his relationship with his current team-mate.
"But equally we respect each other on track as racing drivers and professionals.
"If you were part of the meetings that we have, there's nothing that would lead to the conclusion that there is something wrong with the relationship.
"[Ricciardo] will be a different guy. I don't want to marry him, so I don't have to be best friends with him. But I think we'll get on with each other."
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