Vettel is on the edge of his fourth consecutive world championship, Juan Manuel Fangio and Michael Schumacher was achieved only this position in Formula 1.
"He has got to be right up there, the kind of level he is performing at is unbelievable in many respects.” Horner said.
"We know that Mark [Webber] is a very talented, very quick racing driver and matching him against that, he has been hugely impressive.
"What has really impressed us is that he has continued to develop, and he has continued to grow as he has gained experience.
"That was his 115th grand prix and to have won the races he has [34] is remarkable."
When asked if, in the future, people will put Vettel in the same bracket as Schumacher and Fangio, Horner said: "Should he achieve it, I think they will have to."
Horner is also adamant that Vettel has not achieved success easily.
"He works so hard at it," he said. "What you guys don't see is behind the scenes, and how much effort he puts in, in his preparation, in his training, in the application that he has.
"He is hugely self-critical and he is always looking at areas where he can improve, or where he can be better.
"He will look at this race, and look at things he could be stronger in.
"It is that inward looking he has that keeps propelling and driving him forward."
Source: Autosport
