Indeed, having hinted recently that Jenson Button will be re-signed, McLaren team boss Eric Boullier is now wavering.
"It is a question where I cannot say yes and I cannot say no," he told reporters this week. "We are evaluating and assessing every strategy for the future."
Alonso's single year at McLaren in 2007 ended more than acrimoniously, but team sources have made clear nothing would stand in the way of a reunion with Ron Dennis some eight years later.
The 32-year-old has often sounded frustrated by his title-less five-year stint in red, culminating in yet another disappointing campaign for the start of the new turbo V6 era this season.
McLaren-Honda would be a fresh start and a blank canvas for Alonso's ambition of adding a third title to his tally.
"It is something I am working for and hoping for," he told the BBC earlier this month. "It is not that I'm not happy with two but the third puts you in a list of very important names.
"I think I can carry on long enough to win and to be competitive for some good years," added Alonso. "I don't know how many -- three, five, seven. I don't think it should be any problem."
As far as Ferrari test driver and fellow Spaniard Marc Gene is concerned, however, Alonso is perfectly happy at Maranello.
"Si, si (yes, yes)," he told Spanish publications this week.
"I think since 2010 we have seen the best of Fernando. In 2010, 2012 or this year his driving is perfect," Gene added.
"He is definitely the best driver there is right now in F1; the most complete. And it's a shame this has not been reflected in more titles -- at least two. He deserved them.
"That said, he is happy at Ferrari; he could not be in a better place," Gene added.