Beast Mode is reportedly hanging up his football cleats ... again ... retiring from the NFL after 11 seasons in the league, according to ESPN's Adam Schefter.

The Oakland Raiders running back just turned 33 years old this week -- which is old for an NFL running back -- and "is not planning to play football again."

The timing is interesting ... the 2019 NFL Draft kicks off on Thursday and now Raiders head coach Jon Gruden and GM Mike Mayock can focus on bringing in a fresh set of legs to take over the role.

Lynch is a legend -- he racked up 10,379 rushing yards in his incredible career and 93 total touchdowns ... which would have been 94 if Pete Carroll would have called a RUN PLAY at the end of Super Bowl XLIX!!!!

Marshawn has retired before ... he stepped away from the Seattle Seahawks back in 2016 -- and around that time, we tried to ask him if he would ever come back to the game.

His response is one of the best burns on a TMZ photog ... EVER!!