Pascal Wehrlein has said that he was more than happy to step in at the last minute and test the championship-leading Mercedes on Wednesday.
The German marque turned heads early on Wednesday morning when they suddenly decided against putting Esteban Ocon, also Renault's reserve driver, in the car as per schedule.
Some suspected that Mercedes did not want to give a works rival an information boost by then sending the 19-year-old back to his duties at Renault.
German Wehrlein, who has been loaned by Mercedes to Manor this year, said that the last-minute call-up after Nico Rosberg drove the car on Tuesday was "totally unexpected".
"The team called me on Tuesday night. They couldn't complete their testing programme and needed an experienced driver. So I went back to the track and did a seat fitting," he is quoted as saying by Speed Week.
The result of Wehrlein's running, however, is that world champion Lewis Hamilton is now locked out of the in-season test scheduled for August at Silverstone.
That is because two of the four in-season test days in 2016 must be driven by drivers without F1 race experience, and Hamilton was unavailable to run in Spain because he was walking the red carpet at an event in Cannes.
Wehrlein's unexpected Mercedes test also came just as rumours swirled about Rosberg being in talks with Ferrari about 2017.
Asked if he had the feeling he was auditioning for a race seat, Wehrlein said: "As a driver you always feel like that.
"You can't just sit back, take it easy and hope that somehow you will get a place for the following season. You always have to get everything out of yourself."
The championship continues next weekend with the Monaco Grand Prix.
