Ferrari's decision to give Vettel "priority" at the start of this season soon descended into farce as Leclerc refused to follow team orders in the second race of the year in Bahrain.
Vettel too reneged on a pre-race agreement in Russia and former Ferrari chairman Luca di Montezemolo recently said that the Scuderia will struggle to get the better of Mercedes without clearly defined number one and two drivers.
Leclerc leads Vettel in the standings by 19 points and two places as the Ferrari drivers battle Max Verstappen for third behind the Mercedes duo.
Vettel said: "The ambition is to finish third, obviously we can't finish first and second, so we'll try to finish third.
"I don't think it matters for next year. As a team, we want to make sure that we have the best end to the season that we can. We've been fighting for good positions in the last races. I'm sure we can keep this up."
Crucial in Leclerc's lead over Vettel is a dominance of qualifying performances, with the season head-to-head 10-7 in Leclerc's favour, including a run of nine qualifying 'victories' over the four-time world champion from France onwards.
"Charles has done a very good job in qualifying, I don't think it's right to sit here and not mention that. That needs to be appreciated," Vettel added.
"I didn't have great sessions in qualifying, maybe things didn't come together the way I like, here and there I think I missed out in qualifying for different reasons.
"Overall I can't be happy with how qualifying was this year. The goal is for the final races is to make sure we have a good Saturday and not only a good Sunday."
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