The debate about the cockpit protection concept Halo continues to rage at Hockenheim.

GPDA president Alex Wurz is furious that the teams voted to delay it until 2018, arguing that all the drivers signed a document unanimously supporting an immediate debut.

"I didn't sign anything," Nico Hulkenberg told Germany's Auto Motor und Sport.

"Our drivers didn't either," agreed Red Bull's Dr Helmut Marko.

It was rumoured that Bernie Ecclestone might have moved to appease angry drivers by saying that after tests at Spa and Monza, a 2017 Halo debut might be back on the cards.

However, Hulkenberg said: "You can't change everything again in September. The engineers are now flat out designing the 2017 cars without Halo."

He thinks that a delay until 2018 is the best idea.

"There are too many scenarios that are unknown, so it's good that we're going to test it more," said the Force India driver.

Mercedes team chairman Niki Lauda agrees, saying: "Let all the drivers test it and we'll see what they say. We really don't know if there are visibility problems on certain corners with at certain tracks."

Red Bull's Marko, meanwhile, criticised the recent FIA presentation about Halo that changed the mind of world champion Lewis Hamilton.

"Certain accident scenarios were not even mentioned," Marko said.

The 2016 championship continues with the Belgian Grand Prix on August 28.