Nissan and Porsche are poised to have Pro class entries in the Total 24 Hours of Spa, despite not having cars in the top category for the full season of the Blancpain GT Series, thanks to a caveat in the Intercontinental GT Challenge rulebook.

Both manufacturers are not eligible to enter its cars in the Pro Cup for the Belgian endurance classic, under Blancpain GT rules, as at least two cars must be entered for the full season, and one of them being in the Pro class.

Nissan has two GT-R NISMO GT3s in the Endurance Cup with RJN Motorsport, but is no longer competing in the Sprint Cup this season.

RJN boss Bob Neville told Sportscar365 that he was confident Nissan would have its two Pro Cup entries at Spa, but declined any further comment.

Porsche, meanwhile, has no cars in the Sprint Cup and even lacks a Pro entry in the Endurance Cup, with only the Pro-Am class Herberth Motorsport and Roock Racing confirmed entires so far.

Stéphane Ratel told Sportscar365 the only way around this rule is to enter two cars in the full IGTC season, which expands to a four-race calendar this year.

“Basically, we need to have a written commitment from the manufacturer saying, ‘Yes, we’ll do [IGTC]’,” Ratel told Sportscar365.

“[Nissan] was at Bathurst and are committed to come to other [IGTC] rounds. They would have to do the whole Blancpain GT or whole Intercontinental.”

Even though Porsche hasn’t confirmed plans of entering Spa, speculation has mounted that the German manufacturer is preparing a two-car Pro Cup effort, to be run by Manthey Racing.

Head of Porsche Motorsport Dr. Frank-Steffen Walliser said that a full IGTC program had been under evaluation, especially in regards to a factory supported program at Spa.

“If Porsche wants to come [to Spa] in Pro, I’ll need to receive a message from them saying they’re coming to Sepang, which they did last year, and Laguna Seca, which I very much think they will,” Ratel said.

“I think for Porsche it can happen. If they don’t come [to Sepang] with Manthey they can support Craft and be there. I don’t see it a big problem.”

The SRO boss explained that the full-season mandate has been put into place to protect Blancpain GT’s crown jewel event from turning into an arms race between factory teams.

“We’re very careful in the customer sport nature of GT3,” Ratel said. “There are new manufacturers coming into GT3 that don’t have the customer sport philosophy yet.

“We want to protect the crown jewel. I wouldn’t want it to be won by a manufacturer just popping in.

“Even if I don’t see an immediate risk, I think it needs to be a structure where you need to do a series and have a real customer program.”

John Dagys contributed to this report