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Manny Pacquiao has put an expiration date on his boxing career -- telling TMZ Sports the plan is to fight until 2021 ... and then hang up the gloves for good.

Manny -- who turns 40 next month -- has a big fight coming up against Adrien Broner in January. Since there aren't a lot of guys fighting into their 40s, we asked if he would retire if he lost the fight.

Of course, Manny is super confident and told us losing ain't an option -- but either way, he plans on fighting for 3 more years before moving on to the next phase of his life.

So, what's next for Manny? He's got options.

Not only is he a politician back home in the Philippines ... he also dabbles in music and basketball. Remember, the guy owns his own hoops LEAGUE in his country.

In fact, we spotted PacMan out on the court in Los Angeles where he hit the winning shot during a pickup game at Pan Pacific Park on Wednesday. He ain't exactly Allen Iverson, but he's got some game. Some.