Fernando Alonso urged to extend McLaren-Honda F1 contract

Boullier played a key role in securing Alonso's return to McLaren, which signed the double F1 world champion from Ferrari on a fixed three-year deal that began in 2015.

How to keep Alonso and Button happy

McLaren endured a troubled start to its reformed alliance with engine partner Honda last season, which led to rumours Alonso could take a sabbatical in 2016 if performances did not improve.

Alonso has consistently denied the rumours and reaffirmed his commitment to the project during pre-season testing at Barcelona.

While realising Alonso could walk away from the project at the end of his current contract, Boullier has urged the Spaniard to keep faith if McLaren-Honda is still not ready to challenge for the world championship in 2017.

"We cannot provide the timescale," Boullier told Autosport.

"You cannot say in racing, 'in three years we will be world champion'. The guy who says this will be wrong.

"You can say, 'we will be world champion between three and five years'.

"To this I agree, but you can't say we will be world champions in 2017.

"He [Alonso] would be foolish already to decide to stop after three years."

Boullier believes a culture of transparency within the team is helping to keep Alonso and team-mate Jenson Button engaged with a project that has yet to deliver the expected results.

"By being part of the process and part of a transparent process they will know when we will hit our target," Boullier added.

"So then it's an open discussion - 'do we stay or do we do it within this three years' frame?'"

Boullier concedes Alonso, 34, and Button, 36, are both running out of time to fight for another world championship before their respective F1 careers end, and cannot afford for the rate of McLaren-Honda's progress to regress.

"Sure they have the concern, but the key is to be as transparent as possible and then at least they know where we are," Boullier said.

"They know how much we progress and I think they can see progress. So far we are not too much into the concern of missing the window."

BUTTON 'MORE ENGAGED'

Button came close to walking away from F1 at the end of last season, before recommitting to the final year of his current deal.

McLaren has undergone significant restructuring over the past two seasons and Boullier says Button has become generally more engaged as a result.

"Because he knows the roots of the team he's got naturally the feedback of the team, so he knows who to trust, what to trust, and he knows where we are and what we are doing," Boullier said.

"He wants to win obviously. It's not good enough [at the moment], but JB is definitely more engaged."

Read BEN ANDERSON'S full feature on Fernando Alonso and Jenson Button ahead of the second year of McLaren-Honda's reunion here, or in this week's edition of Autosport magazine.