FC Dallas midfielder Serioux got a straight red card for his vicious foul on Beckham that sparked angry scenes in Los Angeles' 5-1 win.
Galaxy skipper Becks, who was booked during the bust-up, said: "Why did I react like that? Because he could have broken my leg.
"Then he stood there saying 'Welcome to the MLS, baby'."
Becks, 33, could also be in trouble for waving goodbye to Serioux - and blowing him a kiss.