That is the claim of Flavio Briatore, who manages the two-time champion.
He insists the Spaniard will honour his contract with McLaren, which expires at the end of next season, therefore he "will not be in a Mercedes in 2017".
"People always think of Fernando when a top car is free," Briatore told La Gazzetta dello Sport. "But we have a contract and we will respect that."
Alonso is one of a number of names linked with Nico Rosberg's vacant Mercedes seat, following the German's shock decision to retire.
Other top drivers such as Daniel Ricciardo, Max Verstappen, Sebastian Vettel and Valtteri Bottas have also been linked with a move to the Silver Arrows, but have ultimately either declared themselves unavailable, or have been told they will not be moving by their current employers.
Bahrain International Circuit - Winter testing