The four-time Formula 1 world champion has been completely overshadowed by his Australian team-mate behind the wheel of the Red Bull RB10 this year.
Sitting third in the championship standings, Ricciardo has claimed two victories at Canada and Hungary this season and remains the only man to defeat the all conquering Mercedes duo of Nico Rosberg and Lewis Hamilton.
The Aussie has accrued five podiums in response to Vettel's two which has allowed him to open up a 43 point lead over his team-mate in the standings.
Ricciardo also currently leads his more experienced rival 6-3 in the qualifying head-to-head, with the Western Australian boasting an impressive starting berth average of 5.1 from the 11 races so far this year.
Although keen to praise the efforts of Ricciardo this season, Vettel believes the gulf between the two Red Bull drivers is due to a higher rate of reliability issues he has encountered.
“I won't argue with the fact he (Ricciardo) did a great job so far, on my side, we've had plenty of qualifying sessions where we have had some sort of trouble,” said Vettel, who is sixth in the championship standings.
“I do not remember all of them in terms of what the nature was, but we lost out many times because of that, and in the races too, which was getting quite frustrating.
“That's why I am not interested in comparing too much because, on my side, it's not fair to compare.
“Fortunately for Daniel, he had a smoother year in terms of reliability. I'm not saying a perfect year, but way less issues than I had, so I think it's not entirely fair to compare.”
Meanwhile, Ricciardo heads into this weekend's Belgian Grand Prix with momentum in his favour after recording his second victory of the season at Hungary last time out.
“I've just got to keep building on the first half of the year we had,” said Ricciardo.
“It was really nice to get a couple of wins in the first 11 races, so yeah, for confidence, for motivation, for myself and the team it's obviously really high.
“Spa and Monza are circuits which on paper aren't circuits that are going to suit us the most but we're coming in with a bit of momentum so we'll try to pull off a good result here and in Monza and then we've got a few tracks that will really come to us after that.”