The Spanish driver left Ferrari to return to the Woking-based team for Honda's comeback to the sport, but endured a dismal season with an uncompetitive package and poor reliability.

The difficult year even led to suggestions that he could take a sabbatical in 2016 if the team did not improve during the winter.

But Dennis insists Alonso knew what he was getting into, and remains convinced he will enjoy years of success in the future.

"Fernando's contract is of three years' duration - no performance clauses, no nothing," Dennis told the official Formula 1 website.

"He always knew that 2015 would be a learning year. He knows equally well that, together with Honda, we'll make big improvements. So he joined us with open eyes.

"Together with the expertise and experience he's cultivated over the past 15 years spent racing in Formula 1, he still bristles with energy and enthusiasm.

"He's had better years than 2015, obviously; but he knows that great years lie ahead of him, with McLaren-Honda."

Alonso, who drove for McLaren during the 2007 season before leaving after a bitter year, has become a more mature driver, according to Dennis, who hailed the two-time champion's skills.

"Fernando is as hard-working as he is talented, be in no doubt of that," he said. "He's matured enormously since he last drove for us, eight years ago, and he's now one of the most complete drivers I've ever had the privilege of working with.

"He has what I often refer to as the four 'Es' that all racing drivers should aspire to cultivate: energy, enthusiasm, expertise and experience."