Eric Boullier has praised Fernando Alonso and Jenson Button for the way they have responded to McLaren's slow start to the 2015 season.

McLaren has yet to score a point since switching from Mercedes to Honda power, though both the team and manufacturer warned of a slow period of adjustment at the start of the year. There has been clear progress since the season opener in Australia, though not enough to propel the team into the points, and Honda is ready to introduce an upgraded power unit for the Spanish Grand Prix.

Asked how the drivers were responding to a difficult situation, racing director Boullier said: "No, it's not difficult. They are doing a very good job ... I'm very happy. They clearly extract everything they can from the car, no mistakes, it's very impressive to be honest."

Boullier says the patience of his drivers, who have three world championships between them, is down to the fact both men understand the fact the McLaren-Honda partnership is a long-term project to get back to the front of the pack.

"I don't see any issue with motivation with any of them. They see and they feel the progress and they both know how immature the project is and where we go, so they already have a view on short-term, medium-term, by the end of the year or even now we are starting to talk about next year, because we want them to buy into what we are doing but also be critical about where we go. It's good to have different opinions and points of view but they are very motivated, very professional and I have to say I'm 100% happy."