Felipe Massa says Formula 1 cannot introduce Halo until such a time as "proper" tests have been carried out.
Last month Formula 1's Strategy Group voted against running Halo in 2017, but it is still on the table for the following season.
At the time F1 supremo Bernie Ecclestone revealed that there needed to be further tests and development of the cockpit protection device.
And that's a sentiment echoed by Massa.
"It's very difficult to answer without having tested it," the Williams driver told Motorsport.com.
"We need to put it in the car and not just do an installation lap. You need to do a proper test, which is the most important thing they need to start doing. And then you have a proper answer.
"If you put it in the car and do just an installation lap it doesn't work, it's not the right test.
"I think the most important thing is we need to understand if the Halo is really a big step forward. If it's a step forward it would be nice to have better safety in the car.
"But I think the most important thing is people to try it properly. I have never tried it, so how can I answer if it's the best thing or not?
"It would be nice to have it in the car and to try it at to see if the Halo changes anything for the visibility. I don't think they need to not put it in the car because it looks ugly.
"Safety is more important and I think people would get used to is quickly."
The Brazilian added that the decision on whether to introduce Halo in 2018 should be left entirely in the hands of the FIA, not the teams.
He added: "On safety, I believe the FIA needs to be the one to decide. I think on the safety, yes."
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