Veteran journalist Roger Benoit said the Silverstone based team has weighed up paying drivers including Adrian Sutil and Bruno Senna, or an essentially unsponsored talent like Sebastien Buemi.
"With five million, I would be there immediately," Swiss Buemi, currently Red Bull's reserve driver, said.
"But I'm still optimistic."
Also still in doubt is Nico Hulkenberg's 2013 teammate at Sauber, as candidates Esteban Gutierrez and the impressive new Renault World Series champion Robin Frijns, a 21-year-old Dutchman, test the C31 this week in Abu Dhabi.
Germany's Auto Motor und Sport, meanwhile, said the Swiss team Sauber is this week testing a Lotus-style 'double DRS' system.
Fastest on the opening day of the 'young driver' test on Tuesday was Kevin Magnussen, the son of former McLaren test driver Jan.
But team boss Martin Whitmarsh said that with veteran tester Gary Paffett taking over from Magnussen on Tuesday afternoon, McLaren's focus this week is actually on improving the car.
"A lot of the small teams use young driver testing for revenue and a team like ours uses it largely for a range of technical developments," he said.