F1 teams are facing a "big struggle" to make 2018 winter testing following the FIA's late decision to introduce the Halo next season, according to Force India's technical director Andrew Green.

The FIA announced in July that the Halo, rather than the Shield, would be mandatory on cars in 2018 and the cockpit protection device will be an integral part of the chassis structure.

Green revealed at the Belgian GP that Force India's design work is weeks behind schedule and thinks there is a big chance some teams will be absent from the Barcelona tests, the first of which gets underway on February 26, 2018.

Halo confirmed for F1 2018

"It is going to be a big struggle to get to winter testing. It's a big risk teams won't make it," he said.

"We got some information over the break which has allowed us to progress slightly. We are still waiting for some critical information though, which is effectively holding up the chassis design.

From 2018, all F1 cars will be fitted with the Halo cockpit protection device, a decision that has split the world of F1 From 2018, all F1 cars will be fitted with the Halo cockpit protection device, a decision that has split the world of F1

"[The FIA] have given us a general layout of the car installation and racing installation but we are missing all the configuration for the chassis testing. The sign off for chassis testing is the bit we're missing but that is the bit we design the chassis to.

"Every minute that we sit here it's delaying it. The definition came so late. It was big shock to us all when the Shield got overturned and the Halo got introduced. Our development time has been compressed into days.

"At the moment, I don't know if we will make [pre-season testing]. Our schedule has slipped, our release date for the chassis with all the information has come and gone.

"We will have to shorten it somehow, and we work to pretty tight schedules anyway. It is going to be a challenge and we don't know how much we will have to do before we receive a data and do all the work."

While Force India may not make it to Barcelona, midfield rivals Williams are optimistic their 2018 car will be ready for testing, with Paddy Lowe saying: "There is quite a bit of work to do but we think it will be manageable. There are still a few uncertainties there but we'll manage it."

F1 drivers split on Halo

Force India plan to do another Halo test on their present car in a practice session before the end of the season, most probably at the Malaysia GP.

Green thinks the introduction of the Halo will have a limited effect on the aerodynamic performance of the 2018 cars.

"With the new regulations, it would appear that the lower rear wing really helps mitigate the [aerodynamic] problem with the Halo," he said.

"From what we've seen so far, it is relatively useful compared to the Halo on the previous spec of the car.

"We are anticipating it won't be a big aerodynamic performance loss, especially as we are allowed to shroud certain parts of the halo to minimise some of the losses, direct the air flow slightly. It all helps and means we are minimising the downturn."

Despite the race against time to get next year's car ready, Green says Force India would continue to develop their 2017 car as they look to secure fourth in the Constructors' Championship for the second year running.

"It's two separate groups. We've still got lots in the pipeline and lots of developments to put on this car which will hopefully carry over to next year."