Technically, the Spaniard remains under contract to the struggling Maranello team until the end of 2016.
"I'm sure he is very frustrated," Niki Lauda told the Spanish newspaper El Pais earlier this week.
But "he can't just go to McLaren because he has a contract that he can't get out of unless he's sacked. Sometimes you choose a car and you're wrong."
Mercedes team chairman Lauda, however, may not be right. There are at least two recent examples of drivers with solid Ferrari contracts who did not wear red the next year.
Ferrari said in 2004 that Rubens Barrichello would drive for the team in the "2005 and 2006 seasons", but the Brazilian actually raced a Honda in 2006.
And Kimi Raikkonen famously took a sabbatical in 2010, after Ferrari bought out his contract to make way for Fernando Alonso and Santander.
Now, Italian media sources say Alonso might not necessarily drive a red car in 2015, even though Ferrari reportedly wants to extend the deal even further.
The sources, including Autosprint, say Alonso could be free to go at the end of this season due to a contractual performance clause, requiring Ferrari to finish at least third in the constructors' championship.
In Hockenheim, Ferrari fell behind Williams for that position.
Autosprint cited German sources in saying Alonso, 32, has already made contact with Mercedes.
Meanwhile, in the wake of speculation Ferrari might oust the struggling Raikkonen ahead of 2015, boss Marco Mattiacci insisted the Finn is a "driver that Ferrari needs for next year".
That also ties in with the information of the respected Ferrari insider Leo Turrini.
"Maranello has not the slightest intention of questioning Raikkonen's contract," he said in his Quotidiano blog.
On the other hand, Turrini claims Alonso "has not yet responded to the proposal for the extension of his contract".
And not only that, "Ross Brawn will accept a role only as an external consultant", he added.