LeBron James is FURIOUS about Devin Booker's snub from the All-Star Game ... saying the Phoenix Suns star was more than deserving to make the team in 2021.

The Western Conference reserves were just announced Tuesday ... and while huge names like Damian Lillard, Anthony Davis, Chris Paul and Zion Williamson were picked, 24-year-old Booker didn't make the cut.

Of course, Booker is averaging nearly 25 points, 4 rebounds and 4 assists a game ... with the red-hot Suns sitting at 4th place in the conference standings with a 20-10 record so far this season.

Apparently, that wasn't enough for the NBA coaches ... who each voted for 7 reserves to rep their conference in the game.

King James fired off about the snub on Twitter ... and he wasn't the only one.

Blazers guard CJ McCollum also expressed his dissatisfaction with Book getting left out ... saying, Damn @DevinBook really didn’t make it ? That’s craxy . Bruh really cold too smh. Sick world"

LBJ also weighed in on Lillard not being named a starter for the ASG ... saying he's the second most disrespected player behind Booker.

Now, there's still hope Booker sneaks into the festivities and becomes a replacement for AD, who is dealing with a calf and Achilles injury.