Alonso has been linked with a move following Nico Rosberg's shock decision to retire from Formula One with immediate effect. Rosberg's departure has left Mercedes weighing up its options, with Toto Wolff saying Alonso is one of the drivers the team is considering.
However, Briatore insists there is no chance of the double world champion leaving McLaren before his contract expires at the end of the 2017 season.
"Fernando Alonso will not be in a Mercedes in 2017," Briatore told La Gazzetta dello Sport. "Granted, people always think of Fernando when a top car is free. But we have a contract and we will respect that."
Briatore's comments follow a similar stance from new McLaren executive director Zak Brown, who stated his belief Alonso would remain with the team despite the interest from Mercedes.
Wolff recently said Mercedes would need to be "brave" with its choice regarding who replaces Rosberg, having been "compromised" by the late notice given to the team. Alonso had been highlighted as a potential target because Wolff said: "He is a driver I respect a lot. He combines talent, speed and experience. It's all there."
Alonso has also previously been team-mate to Lewis Hamilton at McLaren in 2007, with the pair infamously falling out at the time. His last race victory came in 2013, and the Spaniard finished 10th in the drivers' championship with 54 points this season after scoring fifth places in Monaco and the United States.