It all went down on the set of "Good Morning America" ... when Eli was rolled into the studio in a giant wooden box to break the news to Michael that no future NY player would ever wear his old #92 again.

Check out the video ... Strahan was shocked to see his former QB -- and he was even more surprised when his ex-teammates Justin Tuck and Jessie Armstead joined in too!

The trio explained to Strahan the honor ... informing the former pass rusher that his jersey retirement ceremony will happen on Nov. 28.

To make the announcement even sweeter, they told Strahan the game will be when the Giants play his old rival, the Philadelphia Eagles.

New York later released a statement on the honor, with Giants president John Mara saying, "He deserves to have his number retired as other Giants immortals have, including Mel Hein, Frank Gifford and Lawrence Taylor."

Mara added, "Michael's career was defined by his achievements, his consistency and his leadership. Very few defensive ends played the position as well as Michael."

Strahan -- a second-round pick in the 1993 NFL Draft -- was a BEAST during his 15-year NFL career ... logging 141.5 sacks -- the most in Giants history and the 6th-most ever in the league.

Strahan still holds the record for the most sacks in a single-season (22.5) ... and he also owns a Super Bowl ring -- one in which he earned by famously beating Tom Brady's undefeated Patriots.

"Michael Strahan was a Hall of Fame player and he is a Hall of Fame person," Giants chairman and executive vice president Steve Tisch said.

"Only the very best players get their jerseys retired and Michael is in that category in Giants history and NFL history, as well."