Another win for Khalil Mack against his former team cost him quite a bit ... as the Chargers superstar sustained a gnarly arm injury in the big "Monday Night Football" victory over the Raiders.
The 34-year-old -- who was once traded by the Silver and Black early in his NFL career -- got hurt in the first half of the matchup at Allegiant Stadium in Las Vegas ... when he was trying to tackle Tre Tucker.
The pass rusher went to go wrap up the wideout, but his Bolts teammate collided with him right at the same time -- and the force of the blow appeared to dislocate his elbow immediately.