Marc Lieb and Brendon Hartley are the prime candidates to fill the vacant drives with Porsche for next year's World Endurance Championship.
Porsche LMP1 boss Fritz Enzinger has confirmed that long-time Porsche factory driver Lieb and former Red Bull junior Hartley will test the German manufacturer's 2014 LMP1 contender in the coming weeks with a view to filling the two remaining seats.
Enzinger explained that Lieb, 33, will be evaluated in the Porsche LMP1 gasoline-electric hybrid over the course of two separate tests. A decision will then be made on whether he lands a contract to race the car next year.
"We think that Marc deserves a chance; he is a good guy, but the most important thing is that he is fast," said Enzinger. "He will do the tests and we will compare the data with the other drivers."
Lieb needs to prove himself in the LMP1 because he has exclusively raced GT machinery for Porsche and has little relevant downforce experience from open-wheel cars.
"This is an important point," continued Enzinger. "If he fits in well and he is fast, he will be confirmed as the fifth driver."
HARTLEY'S SIMULATOR APPEAL
Enzinger confirmed that Hartley, who has raced with the Murphy Prototype LMP2 team over the past two seasons, is also in the running for a drive in 2014. He explained that the New Zealander was scheduled to test the car, but wouldn't say whether the drive was dependent on his performance.
Enzinger said that Hartley's simulator experience with Mercedes in Formula 1 made him attractive to Porsche.
"Brendon has done a lot of hours in the Mercedes simulator and that is of interest to us," he explained. "We have a simulator now, but no drivers with experience of that technology."
No decisions have been made on the driver pairings for next season. Enzinger said that this wouldn't be decided until the run-up to the start of next season.
Longtime Porsche drivers Timo Bernhard and Romain Dumas, Rebellion LMP1 prototype regular Neel Jani and outgoing Red Bull F1 driver Mark Webber are the four drivers signed by Porsche so far.