McLaren will announce their 2015 driver line-up tomorrow after calling a media conference at their technology centre in Woking, England.
It has been known for a while Fernando Alonso is to return to the team he left in inauspicious circumstances back in 2007.
Group chief executive Ron Dennis, however, has taken a surprising amount of time over deciding whether Jenson Button or Kevin Magnussen will partner the Spaniard.
Dennis has been criticised for his dithering, in particular after stating at the Italian Grand Prix in September a decision would be made before the final race of the year in Abu Dhabi in November.
Mika Hakkinen, a double world champion with McLaren, told Swiss newspaper Blick that "what is happening at McLaren is unworthy of such a team".
British Racing Drivers' Club president Derek Warwick claimed to the BBC McLaren's treatment of Button has been "disgusting".
Dennis held a board meeting last Thursday with two other primary shareholders in TAG co-owner Mansour Ojjeh and Mahmood Hashim Al Kooheji, CEO of Mumtalakat, Bahrain's sovereign wealth fund.
It has since taken Dennis the last few days to finally arrive at a conclusion, ending the agonising wait for Button and Magnussen.
Only last week Button said: "I just want to get it done. I want to hear the decision as we all do so we can all move on in whatever direction."
At stake is Button's 15-season F1 career, although it is understood he has irons in the fire should Dennis opt for young Dane Magnussen.
The 34-year-old Briton is lined up for a seat in the World Endurance Championship, with Toyota understood to be leading the pursuers.
Button said: "I'm now really comfortable, and whatever happens I will have a great year next year.
"New challenges are exciting, whether it's in Formula One with McLaren alongside an exciting team-mate, or whether it's elsewhere."