Two midfield drivers think Haas is the best team behind the 'top three' Mercedes, Red Bull-Honda and Ferrari.
But he says Haas has jumped ahead.
"I think Haas are currently leading the midfield," he said in Bahrain. "The car looks good all round.
"I also think it's very close but I think the Haas will be better than us in the fast corners."
Hulkenberg said Renault's deficit is "more on the chassis side than the engine side".
Carlos Sainz, who drives for McLaren, agrees with Hulkenberg's assessment about Haas.
"Haas is clearly ahead of all the teams in the middle of the field," he said.
"They are too far ahead, more than half a second, and I think to close the gap we would need to develop at a very high rate.
"According to my opinion, even at the end of the season, it will be difficult for us to compete with them in qualifying. In the race I'm not sure, but in sheer speed, they are really faster than the others," Sainz added.