"It's one of those positions where it could light up your career or put an end to your career very early if things don't go well," Button told reporters ahead of this weekend's U.S. Grand Prix.
"It's a massive risk to be put in the deep end, if you like, with a team that should be fighting for a title.
"But if a driver is willing to take that risk, he has a lot of confidence in himself and his ability.
"It could go one way or another and I hope it goes the positive way," said the 2009 world champion, who made his debut as a 20-year-old with Williams in 2000.
The 21-year-old Dane is the son of former McLaren and Stewart racer Jan Magnussen and will be the first rookie to make his F1 debut with McLaren since Britain's Lewis Hamilton in 2007.
He steps into the seat vacated by Mexican Perez amid high praise and even higher expectations.
If Magnussen has any doubts about what is expected of him then he need only consider the fate of Perez, a once highly touted prospect who has been jettisoned by the former champions after one disappointing season.
The Formula One starting grid is a shark tank and the 33-year-old Button, who has been in F1 the longest of the drivers currently in the sport, knows better than to get too attached to team mates.
Button said farewell to Hamilton, the 2008 champion, last year and will now be on his third different team mate at McLaren.
GOOD FEEDBACK
"It's always sad to see a team mate leave," said Button. "I have never really been that close to my team mates but still you spend a whole season with someone who goes through the same highs and lows that you do.
"It's the same as the end of last year. You build a relationship with a team mate, you learn a lot about each other, gain experience and then things change.
"It's a little bit tough initially but you learn to adapt as we all do in life."
Magnussen has shown all the signs of being a quick learner as well as quick on the track and Button is not about to become anyone's nursemaid.
"If he's willing to learn from the go and picking things up, I don't think so," said Button. "I'm sure he's going to learn from me, I've been in this sport for 13 years but you also learn things from young drivers.
"We've seen his speed in other Formulas and I think the team has been impressed with his speed in the test that he has done.
"The bit for me that is more important is feedback but I've heard his feedback is very good from those tests, which is good that I can believe and trust his feedback."
After a brutally disappointing campaign that has seen McLaren finish no higher than fifth in 17 races so far, the team will be looking for a big bounce back next season when there are major changes and a new V6 engine.
"I've said all year that it's important to have a team mate, especially with the new regulations, that has experience," said Button.
"Kevin doesn't have that but his outright speed is very good and the bit that is more important to me is, from the testing he has done in a Formula One car, his feedback has been very good which has to be very important at the start of the year."
(Editing by Alan Baldwin)
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