's rip-roaring ditties can capture any crowd's attention ... unless the Green Bay Packers are on apparently.

TMZ's obtained video from LB's concert at "Crash My Playa" -- a four-night concert event in Cancún hosted by Luke himself --from Saturday night and everyone seemed super into the music ... except one dedicated GB fan that is.

Instead of taking in the performance, this fan's face was buried in his phone .

.. watching the Pack take on the San Francisco 49ers in the second round of the playoffs -- you can't make this kinda stuff up.

He wasn't in nosebleed seats either -- check out the view! Just feet away from Luke Bryan blasting his hits and getting the crowd fired up. Yep, the concert looked freakin' lit.

Now, we gotta be fair here ... doesn't seem like Mr. Green Bay was blaring the NFL audio, and it was a pretty damn important game -- but, still seems strange to go to the concert if the game's that much on your mind.

Maybe he bought tickets months ago when Green Bay didn't have a snowball's chance in heck to make the playoffs ... before winning their last three games and barely edging out the Seattle Seahawks for the final spot.

Unfortunately for this diehard fan, the Packers game didn't end well for his guys ... with 'Frisco pulling off the late 24-21 victory. Insult to injury alert ... they'll play the Detroit Lions in the NFC Championship game next weekend -- a major rival of GB.

Luke might be singing about "Knockin' Boots" -- but we just hope this fan isn't kicking himself for focusing on a loss instead of the show.