Robert Kubica won't be racing in the World Endurance Championship this year, having ultimateky declined a drive with the Manor LMP2 squad to focus on his F1 commitments with Williams.
The Polish driver mulled boosting his schedule in 2018 with a racing programme with Manor.
The 33-year-old tested the British team's G60-LT-P1 twice recently, and while the successive runs at Aragon went well Kubica felt his interest would be better served by focusing on his role as Williams' reserve driver this year.
"The tests went quite well, but the problem is time," Kubica told the media at a sponsor's event in Warsaw.
"I will have very little [time], so I decided not to compete in the WEC. I will focus on my role at Williams.
"During the past 45 days, I've spent two days at home and I don’t really know anymore where home is – I’d love to race but I have to be rational."
Kubica's tasks with Williams this season include a heavy programme of simulator work back at the team's Grove factory base in addition to a series of Friday free practice runs at specific Grand Prix.
Manor's Graeme Lowdon confirmed that Kubica's workload with Williams coupled with a WEC drive would have likely extended the Pole's already heavy schedule.
"Robert is a good friend of the team — he helped us out in testing and we gave him the chance to see what the car was like," said the outfit's sporting director.
"If he was looking to race in the WEC, we'd have have been very happy to have him. His duties at Williams are quite extensive, so I think a WEC programme on top would have been an awful lot of work."