76ers' Michael Rubin Joel Embiid's a Tough-Ass Dude ... You See That Busted Finger?!

TMZ Sports Presents: "How To Impress Your Boss" ... starring Joel Embiid!

Today's lesson ... when you dislocate your finger, SNAP IT BACK IN PLACE AND BALL OUT!

The strategy worked, judging by our conversation with Philadelphia 76ers partner Michael Rubin, who raved about his star player's toughness after the freak injury.

As we previously reported, Embiid busted his digit during Monday night's game against the OKC Thunder, but taped it up and went back in the game ... and led the 76ers to a big-time win!

"He was a warrior," Rubin said ... "That was one of the ugliest things I've ever seen!"

"It just shows how tough and aggressive he is and how badly he wants to win."

Embiid has been ruled out for Thursday's game against the Boston Celtics -- and he's following up with a specialist. Rubin wouldn't elaborate on the injury, but 76ers fans are obviously concerned.

There's more ... Rubin says he's been talking with Ben Simmons about the fires in Australia -- and his star player inspired him to open up his wallet and donate to the relief efforts.

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