Don't underestimate Justin Bieber -- 'cause if push comes to shove with Orlando Bloom (again), NHL legend Jeremy Roenick says he's taking The Biebs ALL DAY.
Turns out, Roenick is a huuuge Justin Bieber fan ... like, big ... and says JB's got too much going on in his life to worry about Bloom getting cozy with his ex-girlfriend Selena Gomez again.
Remember, Bloom and Bieber got physical over Selena back in 2014 -- when an altercation broke out at a restaurant in Ibiza.
Well, Roenick says if the two come to blows again .