Press Association Sport understands that although a deal has not yet been signed by McLaren development driver Magnussen, the 21-year-old Dane will replace the under-performing Perez and partner Jenson Button for next season.
Although team principal Martin Whitmarsh has stated that "we haven't signed contracts with drivers", behind the scenes McLaren are known to have made their decision, with Magnussen given the nod.
Discussions over a contract are currently ongoing with Magnussen, who was recently crowned Formula Renault 3.5 Series champion - beating another McLaren rising star in Stoffel Vandoorne by 60 points - although are expected to be concluded swiftly.
It is understood McLaren have opted to promote Magnussen, rather than retain Perez, following extensive analysis of performances.
Although McLaren produced one of their worst cars for many years this season, one that is set to complete the campaign without a podium for the first time since 1980, Perez has only scored 35 points to Button's 60.
The 23-year-old has also been out-qualified nine times to eight by the Briton, a slender margin perhaps, albeit with Button renowned in Formula One for not being one of the quickest over a flying lap.
McLaren had hoped Perez would prove a reliable replacement for Lewis Hamilton, quickly moving to sign him last year following the latter's departure to Mercedes.
Perez, however, has failed to show the promise suggested during his time with Sauber last season during which he notably scored three podiums, including runner-up in Malaysia and Italy.
Although Perez was fifth in India at the end of last month, matching McLaren's highest finish this year achieved by Button in China, the team have been underwhelmed by what they have seen.
In particular, time in the simulator of late has shown Magnussen to be quicker than Perez, and this has played a part in their thinking.
It means for the first time since Hamilton in 2007, McLaren are to promote an unproven driver into the big time.
There is some concern given the extensive regulation changes for next season, with the cars due to become even more complicated with the arrival of the 1.6-litre turbo charged V6 engines, replacing the current 2.4-litre V8s.
Speaking recently in Abu Dhabi, however, Magnussen maintained such a step up would not be an issue.
Magnussen, son of former F1 driver Jan, said: "Whenever I'm asked about Formula One, I always reply that, yes, I feel ready.
"I look at this way - I've done everything I could to prove myself in World Series."
Perez's future is unclear, although he has been linked with a drive with Force India for next season.