The tragic shooting in Las Vegas hit close to home for UFC superstar Cody Garbrandt ... who tells TMZ Sports a very good friend of his wife was shot twice while attending the Route 91 Harvest Fest.

Cody says his wife, Danny Pimsanguan, lives on the Vegas strip -- and was "hysterical" knowing several of her friends had attended the music festival ... including one who was rushed to the hospital with multiple gunshot wounds.

Garbrandt tells us he can't stop thinking about victims of the massacre ... and is urging UFC fans to join him and other fighters in Vegas to donate to blood drives.

The bantamweight champ even says he'll send out swag to volunteers who tag him on social media because it's important to "give back in such a crucial and horrific time."