© Sutton Images Enlarge

Jenson Button admits he was "surprised" by McLaren's decision to replace Sergio Perez with Kevin Magnussen due to his new team-mate's lack of experience.

Magnussen was confirmed as Perez's replacement on Thursday morning and will become McLaren's first rookie driver since Lewis Hamilton, with Hamilton able to enjoy unlimited testing before his debut season. Button said the move had come as a surprise but added that he sees the strengths that Magnussen will bring.

"I'm always surprised by Formula One and things that change," Button said. "I was surprised last year when Lewis decided to leave and I think the same now. But it's what Formula One is like; things change and we learn to adapt. I've said all year that it's important to have a team-mate - especially with the new regulations - that has got experience.

"Kevin doesn't have that but I think his outright speed is very good and the bit that is more important for me is from the tests that he's done in an F1 can and looking at the data and what have you his feedback has been very good, which is going to be very important at the start of the year. We get equal days in the car and it's important that his feedback is good, having confidence in that. It is an exciting challenge for all of us next year and having Kevin on board with his speed and his determination I think is good for the team."

However, Button also challenged Magnussen to be ready to deliver from the start of pre-season testing in the face of new regulations.

"I know a little bit about him and the way he goes racing and his speed but also the way that he works with the team. He's also been with this team for a long time so he gets to spend time in the simulator and really understand how a Formula One driver works within a team and the input and feedback that you need to give a team. He needs that and he needs to learn that very quickly if he doesn't have that already, because we need to start from the first day of testing to be strong and already start developing the feel of everything in terms of the engine, the power unit and also the car."

On Perez, Button said he had been somewhat harshly treated having shown clear progress throughout the season.

"In terms of driving I think he's come a long way this year. I think he's learned a lot, he's put in some good performances. The one that stands out is obviously India. It's always difficult to compare yourself to someone else when you've had issues in a certain race but India you would say he did a very good job. And I think the way that he's learned throughout the year and improved himself in terms of speed, in terms of being a racing driver, developing the car, tyre management and what have you; he's really picked up a lot this year and learned a lot. He's definitely been on a steep learning curve."

© ESPN Sports Media Ltd.