Hulkenberg plays down his chances of replacing Vettel this season
Quadruple world champion Vettel is still struggling for form after being ousted by Ferrari, amid rumours he might not even see out the full 2021 season.
But when asked if he thinks stepping into Vettel's cockpit before the end of the season is a realistic expectation, the German said: "No, I don't think so.
"I think he'll end the season there," Hulkenberg, who like Vettel is 33, added.
"He still needs some time and is not feeling great in the car yet. You can see that on the stopwatch. But that's not my decision anyway," he said.
"I don't think these cars suit Sebastian very well," said the Australian. "They're not his type of car.
"He likes cars with a lot of grip, a lot of downforce, and he's a very delicate driver, with a lot of feeling for the car.
"But when there is less grip, with the Pirellis, the cars give the driver less confidence and they really don't suit him. That's a problem for Seb, because look at Hamilton - he's always strong.
"You can also see that he's getting tired - he put a lot of effort into Ferrari," Webber said. "People think I enjoy seeing him suffer but no, I'm not happy.
"I want to see him do well because honestly it's very strange seeing him so different to the way he was. But this is F1, we can't complain about it and we can't make excuses for drivers who don't perform.
"Formula 1 is the pinnacle, so you have to celebrate drivers who are doing well like Norris, Leclerc or Max. If you're a driver in the final part of your career or you're suffering, you also have to say it like it is," Webber added.
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